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Senna Build Guide by ayoshe

Support gold

"First rule to being a sentinel...." S11.7

By ayoshe | Updated on April 7, 2021
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Glacial Augment
Magical Footwear
Biscuit Delivery
Cosmic Insight

Legend: Alacrity
Presence of Mind

+10% Attack Speed
+9 Adaptive (5.4 AD or 9 AP)
+6 Armor


1 2 3 4
LoL Summoner Spell: Barrier


LoL Summoner Spell: Flash


LeagueSpy Logo
Support Role
Ranked # in
Support Role
Win 51%
Get More Stats


Threats & Synergies

Threats Synergies
Extreme Major Even Minor Tiny
Show All
None Low Ok Strong Ideal
Extreme Threats
Ideal Synergies
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I began playing League of Legends since early season 6 (primarily on the North American, Korean and Oceanic servers), while playing competitively for the first time in season 9. I was introduced to Senna when she was revealed live on the PBE servers and she quickly became one of my pocket picks.

Of course, I'm still searching for new builds/items that might work well with her, so I'm constantly learning as I write this guide. I hope you learn something new while reading as well!

Disclaimer ! I'd like to emphasize that this is solely based off my insights and personal experiences in the bot-lane, so some of the information in this guide may or may not be relevant to you. This guide lacks credibility since I am, after all, low-elo. Additionally, I will unfortunately only be covering the supportive side of Senna and how to play her as the role of a support if you haven't read already. I apologize if this does not contain information regarding other roles Senna can play. This is also my first guide, so feedback is very much appreciated.

Some content may be missing because this guide is still a minor work-in-progress.

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AS OF RIGHT NOW, I find her gameplay addicting and thoroughly enjoyable, however there are several other aspects to her that make her a good pick. Senna is an eccentric marksman/enchanter hybrid designed specially in a way for her to be versatile and adaptable to building both damage, support or a fine blend of both. She does great deal of damage while providing utility in her kit, making her viable in a variety of roles that other champions may not be as flexible to. Although she is strong as a support, her potential as a bot laner is often overlooked when she does in fact scale equally as well. If you are new to the game, or even a returning veteran, I would always recommend adding Senna to your champion pool because she is easy to learn, strong and overall satisfying to pick.
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+ Scales infinitely as time goes on
+ Global AoE shield/execute
+ Team Camouflage
+ Decent healing
+ Reduced cooldown on Piercing Darkness with autos
+ Basic kit, easy to master

Senna is still currently very strong to play. She's considered as a "secondary ADC" on the team due to Absolution, which also deals a percentage of the target's current health. Whether you choose to build complete support/damage her heals with Piercing Darkness, regardless, remain helpful amongst your team. Not to mention, she can camouflage your entire team for unexpected roams or flanks with Last Embrace!

- Cannot peel
- High mana costs
- Requires good positioning
- Weak heal early
- High CD timers, especially for Dawning Shadow
- Does not have an escape

Senna also does take some getting used to, especially with her very high mana costs (making Piercing Darkness heals not worth spamming in lane and her slow attack-speed. This also makes it difficult to kite, thus making positioning very important to Senna's playstyle so you can abuse her range and support your team from the back-line. With time and practice, Senna's weaknesses will become much easier to play around.

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I only want to highlight a few parts that are core and compliment her set of abilities the best. The rest is mainly personal preference, whether you'd like to go into hybrid, full-damage or support. This should just be used as a general guideline as to what you want to take. As of right now (11.2), the best runes to run are Glacial Augment, and a very situational maybe Grasp of the Undying. If you plan on going full Enchantress, I think Summon Aery is also a viable option.

Would also love to kindly note that I categorize runes as "major" or "minor" depending on the flexibility of the pick. For example, the Inspiration tree has a lot of situational picks, thus why a lot of your options are "minor", whereas your options in the Domination tree are much more limited, so options there are "major".







KEYSTONE Glacial Augment
- Glacial Augment is probably the best keystone right now for Senna. It allows for some nice slows that may ease your struggle from trying to obtain souls from Absolution. It’s also just nice in general for all sorts of reasons (e.g. kiting), especially if your team has some strong CC already and just require a slow to engage.

- In this case, Sorcery secondary works very well because now that you have a slow in your abilities, you can harass even more with Scorch, or get some cooldown reduction with Transcendence. Domination could also work because of Cheap Shot and Ultimate Hunter, or even Taste of Blood for sustain. Font of Life may not be very ideal, but it could work, especially because you also have a root.

- Support or damage, your offense/flex/defense will remain two adaptive forces and armor. You can take Time if you feel that your cooldowns are too long, it synergizes well with Cosmic Insight so that you get 6% cooldown reduction in the early levels. There is no reason for you to take Axe because Senna doesn't scale well with it and you will not be building attack-speed in any situation.

  • Magical Footwear: Recently I have been experimented using this rune instead of Perfect Timing and have found that it is indeed a good pick. The movement speed bonus is really nice and will always be beneficial to Senna because she is squishy and has no escape. I think Perfect Timing isn't that good because I personally don't find the right time to use it and the selling value is only 20 gold.
  • Future's Market: Biscuit Delivery since it provides some extra sustain in lane to keep you healthy, and adds to your maximum mana pool which Senna greatly benefits from. Since you do not have sustain aside from Piercing Darkness, Biscuit Delivery nullifies the issue since it has very good potential in early levels. I take Future's Market on a lot of supports otherwise when I come across the Inspiration tree because supports struggle with gold income, even with changes to the support items so that we don’t need to upgrade our item with gold. Future's Market is also handy if you are behind in lane, because you can always go in-debt, but I still think Biscuit Delivery is currently the best option. Either of the two are situational. Minion Dematerializer is completely useless to you because you won’t be taking Steel Shoulderguards to execute minions, nor will you be trying to farm minions.
  • Cosmic Insight: this is another one of my favorite runes because it allows you to exceed the cooldown reduction cap and automatically gives you 5% cooldown reduction at level 1. I can see Approach Velocity being viable due to the fact that you have an extra CC tool which can help chasing or just trading quickly with Glacial Augment. However if you are unused to having long cooldowns on your abilities, the cooldown reduction gained is still fairly helpful. Time Warp Tonic which has excellent synergy with Biscuit Delivery, however it is a niche pick because you won’t be needing pots later on throughout the game and it puts a cooldown on your potions which isn't very ideal, whilst Cosmic Insight and even Approach Velocity can always help you from the start till the end of the game.


KEYSTONE Grasp of the Undying
- Grasp of the Undying has recently surfaced as a new Senna build centric around extra survivability for Senna. It is used as a tool that amplifies Senna's crowd control ability. I've recently been experimenting with this keystone and I have to say, it can be useful in many scenarios, unlike Glacial Augment which essentially does the same thing, but sacrifices your ability to endure fights.

- There are various secondary trees you could go for depending on your playstle, but Precision is most commonly taken for Presence of Mind which aids you in your mana hungry issues, along with Legend: Alacrity or Coup de Grace. I personally prefer Presence of Mind and Legend: Tenacity, however, you could also go Domination for Cheap Shot since this requires you to build Frozen Mallet at some point. This is a really adaptable build dependent on your matchup and your own playstyle.

- Support or damage, your offense/flex/defense will remain two adaptive forces and armor. You can take Time if you feel that your cooldowns are too long. There is no reason for you to take Axe because Senna doesn't scale well with it and you will not be building attack-speed in any situation.

  • Grasp of the Undying: This is taken preferably in team comps that do not favor Senna (e.g. vs. Thresh, Pyke, engaging supports), however you can also take this in every and any matchup. It is made to counter Senna's biggest weakness, which is her squishiness, whilst reinforcing her ability to put out CC. She can then resume applying her presence in lane, making her strong like she was before. The downside is she doesn't deal as much damage, but it is still worth at least trying out since it's very consistent in spite of this. I'd like to highlight that the whole point of Grasp of the Undying is building health since you now deal damage based on your health. Lethality should never be your priority when trying this build.
  • Font of Life: is my go-to when I decide to play this build, because it is the only rune that I see beneficial for Senna, since Demolish is not all that helpful in my games, and Shield Bash can't really be utilised unless you use Dawning Shadow which wastes the rune's potential. There's no real explanation to this, it's just overall beneficial for your team, especially if you land a good root.
  • Bone Plating: Whenever I go the Resolve tree, I tend to go for Bone Plating since it is overall good rune that can prevent you from losing major trades early on or getting 3-shot in both engage match-ups and matchups against enchanters. Conditioning is not all that helpful even if you're going tank, because you don't need the extra armor. Second Wind in my opinion is not really worth taking because you can always heal back with Piercing Darkness or Biscuit Delivery.
  • Revitalize: this is such a good rune. I think that the small percentage buff to your heals is really good and the rest of the runes just don't compare. Please just take this, it will make your life easier. The alternative would be Overgrowth, which adds on to your health meaning you can soak up more damage.

KEYSTONE Summon Aery
- Summon Aery is another viable keystone for Senna right now, because taking other runes can force you into playing more aggressive, like Dark Harvest and Fleet Footwork, while whatever you build after Summon Aery is flexible. If you like to play Senna full support style, these set of masteries might be to your liking.

- I usually take Inspiration or Resolve secondary because I feel that those two mastery trees synergize better with Summon Aery. You can choose whichever necessary, for instance, a seemingly winnable lane might prompt you to take Magical Footwear or Presence of Mind. It really depends on the situation and what may be helpful to you. Against a poke lane, Resolve secondary can help you with its defensive options like Second Wind and Bone Plating.

- Support or damage, your offense/flex/defense will remain two adaptive forces and armor. You can take Time if you feel that your cooldowns are too long, it synergizes well with Cosmic Insight so that you get 6% cooldown reduction in the early levels. There is no reason for you to take Axe because Senna doesn't scale well with it and you will not be building attack-speed in any situation.
  • Manaflow Band: helps Senna stay mana healthy in lane and the 250 mana is easy to stack because you only need to hit the enemy a total of ten times. I find the bonus mana regeneration also very strong because Senna's mana bar is usually gone after using a few abilities.
  • Transcendence: this rune is mostly based on personal preference. I think that Absolute Focus is also a viable choice here because you'll get an AD bonus for the amount of health you currently have, so I would take Absolute Focus if I am confident about the lane. In team-fighting, you'll also be in the back-line for a majority of the fight, so the adaptive damage you receive is still relatively decent. Transcendence, on the other hand, can give you cooldown reduction in the early levels and some adaptive force if you overcap the cooldown reduction limit.
  • Gathering Storm: again, this is very dependent on how you personally play the game. Gathering Storm is a good choice for Senna due to her late game scaling. Waterwalking is quite underrated in my opinion, because now that the meta has shifted towards becoming more centric on dragons and objective control, the buff you get when contesting/fighting in the river is actually decent. It also helps if you plan to roam a lot. Scorch gives some bonus damage early game and helps with laning harass. It could potentially give you a kill when you use Dawning Shadow or help you win a trade.

KEYSTONE Dark Harvest
- Dark Harvest is a scaling keystone that works wonders late-game. Now it's more of a 4fun type of build. It was previously my personal favorite because of how satisfying it was to play with this keystone. (Ever since I've discovered the Glacial Augment playstyle, I haven't gone back to Dark Harvest.) A severe downside is you miss out on the shield bonus from Summon Aery and the cooldown is long if you don't get the kill reset.

- I usually take Precision secondary because I enjoy taking Presence of Mind and Ultimate Hunter from takedowns with Dark Harvest. For me, Sorcery is situational because Gathering Storm is also a scaling rune that synergizes well with this Domination rune path, however you do miss out on some supportive options like Revitalize which does have equally as good synergy as Dark Harvest with Dawning Shadow. Regardless, the secondary tree is always based on your situation and playstyle.

- Support or damage, your offense/flex/defense will remain two adaptive forces and armor. You can take Time if you feel that your cooldowns are too long, it synergizes well with Cosmic Insight so that you get 6% cooldown reduction in the early levels. There is no reason for you to take Axe because Senna doesn't scale well with it and you will not be building attack-speed in any situation.

  • Dark Harvest: this keystone is something that you might not want to take against tanky champions because it is not a stabilized build. This is mainly for those who like to play Senna as a secondary ADC/support against squishy champions. Dark Harvest works really well with Dawning Shadow and lets you pick up some kills in the early game, plus you can get some early stacks from poking. It is a niche pick right now, but doable.
  • Taste of Blood: enables some sustain in lane against champions who may poke you a lot. Although the cooldown is 20 seconds long, it works just fine. An alternative would be Cheap Shot for some bonus damage when you land a root with Last Embrace. Sudden Impact will not work at all because Senna has no mobility and cannot proc it.
  • Zombie Ward: This is a good rune to take because you might run out of wards, and this still provides vision while not counting towards your active wards. This means that if you buy an Umbral Glaive, a ward will automatically spawn and you won’t have to waste placing a ward there. This does not excuse you from not warding, however. It is just a good tool that works well with Senna support.
  • Ultimate Hunter: this is the best choice out of all of the other ones. Of course, you might want to run something like Ingenious Hunter because of items that have actives, such as Youmuu's Ghostblade and Mikael's Blessing as well as wards, or even Relentless Hunter for the bonus out-of-combat movement speed, however the cooldown reduction on Senna’s ultimate is just too good of an oppurtunity to pass up because that enables you to have your ultimate 30 seconds faster when you’ve hunted all five enemies, as well as an extra 5%. If by some chance your team manages to get Cloud drakes, you will be able to spam your ultimate!


KEYSTONE Fleet Footwork
- Fleet Footwork is usually taken by ADC’s because it keeps them healthy and enables them to make aggressive trades. Likewise, Senna can take this, but I recommend Fleet Footwork for somebody who prefers to build complete damage.

- This is mostly based on personal preference rather than something situational. I prefer to take Domination for the cooldown reduction you get from Ultimate Hunter helps your ultimate recharge faster, allowing you to use it in coordination with possibly Coup de Grace.

- Support or damage, your offense/flex/defense will remain two adaptive forces and armor. You can take Time if you feel that your cooldowns are too long, it synergizes well with Cosmic Insight so that you get 6% cooldown reduction in the early levels. There is no reason for you to take Axe because Senna doesn't scale well with it and you will not be building attack-speed in any situation.

  • Presence of Mind: Presence of Mind used to be my go-to on Senna before it was revamped for restoring / increasing your mana instead. Out of the three, it is strong with Senna because of how costly her abilities are when it comes to mana. Triumph could work for surviving a devastating Ignite from the enemy support after you get first blood. Overheal is also alright, but the shield is not that useful to Senna because of how small it is in the early game. I like taking Overheal if I decide to take Legend: Bloodline because the sustain altogether is really nice.
  • Legend: Bloodline: this is what I’ll go normally, unless the enemy team has a hard CC team like Leona, Ekko or even Morgana. For the excess critical strike chance collected, Absolution converts a portion into lifesteal, so this gives you more lifesteal on top of capping 100% critical strike chance. Legend: Tenacity is another good rune that I swear by. In conjunction with Mercury's Treads, the CC reduction is pretty handy. Legend: Alacrity is not viable at all here because it hardly does anything for Senna.
  • Coup de Grace: a lot of the time this will be your main rune pick because it can help execute enemies with Dawning Shadow very easily, or just dealing damage in general. Cut Down is a viable option if you’re against a very tanky team composition and require the bonus damage.
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- Barrier is a really underrated summoner spell that can save you in a fight or from a bad trade. If the enemy support takes Ignite (which is likely in most games), you'll be able to negate some of the tick damage with Barrier without having to burn your carry's Heal to save your life. The cooldown is also relatively short compared to the other summoner spells viable.


- Exhaust is a useful defensive summoner spell used to negate burst damage from an assassin/damage composition, such as when a Zed decides to cast Death Mark, or when Master Yi uses Highlander right before Alpha Strike. While it does have a slightly longer cool-down than Ignite, Exhaust is also much more effective on Senna due how it reduces 40% damage reduction from the target as well as its casting range.


- Ignite gives early lane kill-pressure and reduces healing and is useful if you play very aggressively. It's good against squishy and/or healing champions, such as Soraka, Yasuo, Olaf, Pyke, Aphelios et cetera. It falls of late-game but can still be used if you for some reason cannot buy an Executioner's Calling.

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I do not update abilities because it is cumbersome, so if some of the information is wrong, it is simply because I just copy these from the description. Please hover over each ability if you are unsure of whether or not everything is up to date. As of now (10.23), I have updated everything accordingly.
Absolution (preview) (Passive)

COOLDOWN: 6/5/4 seconds on each target at levels 1/6/11

INNATE - WEAKENED SOUL: Senna's basic attacks on-hit and damaging abilities on enemy champions apply Mist for 4 seconds, refreshed to 0.75 seconds if Senna starts winding up a basic attack on them. If Senna applies Mist to the same target twice, she collects it, dealing 1% − 16% (based on level) of target's current health Attack damage bonus physical damage, and making the target immune to further Mist applications for a few seconds. Champions and large monsters that die near Senna spawn a Mist Wraith for 8 seconds. Epic monsters spawn 2 Mist Wraiths instead. Minions and lesser monsters have a 22% chance to spawn Mist Wraiths, which is reduced to 8.33% chance on those that Senna kills. Senna can basic attack a Mist Wraith to destroy it, gaining 3 gold and collecting its Mist.

INNATE - ABSOLUTION: Each stack of Mist grants Senna 0.75 bonus attack damage. For every 20 stacks, Senna also gains 25 bonus range and 10% critical strike chance. Upon exceeding 100% critical strike chance, Senna converts 35% of the excess into life steal.

INNATE - RELIC CANNON: Senna's basic attacks deal 20% bonus physical damage on-hit and grants 10 / 15 / 20% of the target's movement speed as bonus movement speed for 0.5 seconds on-hit (level 1/6/10).

Piercing Darkness (preview) (Q)

RANGE: 600-1300 (Based on Mist)
COST: 70 / 80 / 90 / 100 / 110 mana
COOLDOWN: 15 seconds
After a brief delay, Senna fires a spectral laser in the direction of the target unit, healing herself and allied champions in a line for 40 / 70 / 100 / 130 / 160 (+0.4 per bonus attack damage) physical damage. Allied champions hit are healed for 40 / 60 / 80 / 100 / 120 (+0.4 per bonus attack damage)(+25% of ability power) health.[/size]

  • Upon struck, enemy Turrets, Wards, Absolution Mist Wraiths and any other attack-interactive units are considered basic attacked once, while champions and Turrets take on-hit effects (with all turret-specific rules applied).

  • Basic attacks reduce Piercing Darkness' cooldown by 1 second.
  • Effect radius of 1300.

Last Embrace (preview) (W)

RANGE: 1175
COST: 50 / 55 / 60 / 65 / 70 mana
COOLDOWN: 11 seconds
ACTIVE: Senna throws a globule of Black Mist in the target direction, dealing 70 / 115 / 160 / 205 / 250 (+ 70% bonus AD) physical damage and sticking onto the first enemy hit. After a 1 second delay or when the target dies, the Black Mist spreads out of the target, rooting them and nearby enemies for 1.25 / 1.5 / 1.75 / 2 / 2.25 seconds.
  • Effect radius of 280.

Curse of the Black Mist (preview) (E)

COST: 70 mana
COOLDOWN: 26 / 24.5 / 23 / 21.5 / 20 seconds
ACTIVE: Senna surrounds herself with an aura of mist and gains camouflage for 6 / 6.5 / 7 / 7.5 / 8. Basic attacks and abilities briefly remove the effects of camouflage.

WRAITH FORM: Gain Camouflage. WRAITH FORM: Gain camouflage. Enemies will gain obscured vision of Wraiths moving outside of the mist. Performing a basic attack or casting an ability removes Wraith Form, which cannot be regained for 2 seconds. Senna and allies camouflaged by Curse of the Black Mist also gain 20% bonus movement speed.
  • Effect duration of 6 / 6.5 / 7 / 7.5 / 8.
  • Effect radius of 400.

  • Camouflage detection radius at 280.

Dawning Shadow (preview) (R)

RANGE: global
COST: 100 mana
COOLDOWN: 160 / 140 / 120 seconds
ACTIVE: Senna reveals herself before firing two beams of spectral light in the target direction, granting sight of the area briefly along its path. The center beam deals 250 / 375 / 500 (+ 100% bonus AD) (+ 50% AP) physical damage to enemy champions hit and afflicts them with Mist.

The broad beam shields Senna and allied champions hit for 120 / 160 / 200 (+ 40% AP)
(+ 1.5 per Absolution Mist collected) over a 3 second duration.

  • Cast time of 1.3.
  • Width of 320 / 2400.

  • Speed of 20000, it casts instantaneously.
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Senna is a relatively laid-back champion who isn't mechanically demanding, making her perfect for those of us who have slow reaction timers.

I will only be going over simple combos and a few tricks because of so.

  • Interactions: Last Embrace
  • You must Flash after casting Last Embrace for it to go in the desired direction. Otherwise, it will be cast in accordance to the direction you used Flash.
  • When you cast Last Embrace on a minion and it kills it, enemies within the radius are rooted instantly and there is no delay. For enemies like Yasuo, regardless if he uses Sweeping Blade or not, he will be rooted in place.
  • Flash Last Embrace is a good combo that raises your chances of rooting the enemy because it is less predictable and leaves little time for a reaction in between the casting.
  • Interactions: Curse of the Black Mist
  • This is not an escape tool, but more-so a disengage tool.
  • When you are revealed (whether through Scryler's Bloom or a Control Ward), your camouflage is disabled, however the movement speed buff still remains active.
  • You can use Curse of the Black Mist to detect Control Wards because it disables your camouflage. This also works for enemy champions, however it is close to face-checking so I wouldn't recommend this.

Your primary combo includes auto-weaving after every ability. I think it is the most effective way to play Senna with this strategy because she deals plenty of damage with her autos, you can cancel the animation of Piercing Darkness through doing so, and you can lower the cooldown on Piercing Darkness which you'll most likely be spamming in fights.

A > Q > A
Early Trading
Piercing Darkness is a really cool ability because it lets you cancel the animation so that you can sneak an extra auto in. An auto-attack followed by a Piercing Darkness enables you to collect a mist stack from Absolution, while also winning the trade ( Electrocute here gives a small amount of burst while using this combo).

W > A > Q > A
Early Rotation
When you land a Last Embrace, this will be a good chance to engage on an enemy. This is basically the first combo but only added with Last Embrace. You can also use Curse of the Black Mist for a disengage, however I think that this wastes too much mana and you can get away with the movement speed collected after Absolution.

W > A > Q > A > R
Full Rotation
The same combo as before, now added with Dawning Shadow for the execute. If necessary, you can auto-weave after using Dawning Shadow. This is also your most common go-to in fights.

Q > R > F
This is a play with less functionality, but it looks cool and is nice for styling on your enemies. It is for the purpose of executing only, however in this case you will also be able to collect an extra Mist stack before they die.

A > R > F
Quick Execution
This fast combo may work when you are low on health and can fight the assassin who is chasing you. This makes use of the animation cancelling mechanic from Senna's Dawning Shadow. Unfortunately, it doesn't let you collect the Mist stack from Absolution, but it's still worth learning.

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In summary, the current best Mythics are Kraken Slayer (from the currently trending build, Eclipse, Divine Sunderer, and Moonstone Renewer. Manamune is now a pretty good buy, while Sheen items are not worth investing.

+ To Buy
This will outline several core items that are worth purchasing and give you advice on how to build Senna. I will later go through a few items that I have seen beginner Senna's buy and why those are not viable/less strong on Senna than these choices.

Spectral Sickle
Spectral Sickle is the AD equivalent of Spellthief's Edge, which was previously built on Senna prior to the passive change. It is also the only gold income item that you will be buying.
Boots of Speed
Boots tend to be very situational that there really isn't one boot choice that you must consistently stick to. For example, vs a heavy mage team composition, you'd want to buy Mercury's Treads, and if their ADC is fed, you'd want to buy Ninja Tabi.
Boots of Swiftness
These are the most commonly upgraded boots for good reason. They provide slightly more speed than the rest of the boots and reduce slows on movement speed. Additionally, they are relatively cheap, meaning that you can upgrade your boot tier early on for an advantage against your enemies.
Ionian Boots of Lucidity
I usually suggest building Ionian Boots of Lucidity if you are building full support, because these synergize very well with Transcendence from the Sorcery tree because of the ability haste Ionian Boots of Lucidity gives. This combined with Cosmic Insight also reduces the cooldown on your summoner spells by 15% total. ]I've found buying Ionian Boots of Lucidity overall the best boot choice because Senna benefits greatly from ability haste.
Boots of Mobility
These are roaming boots, however I also frequently buy them as opposed to the other boot choices. Mobility Boots allows you to roam pretty easily early-mid game. I no longer build Mobility Boots unless I am far ahead and planning to roam (if so, I sell these for Ionian Boots of Lucidity after 20 minutes.) It's just too situational.
Previously, Manamune was slightly costly, however with the changes made with Tear of the Goddess I think that it is a viable item, as you can easily stack tear and buy Tear of the Goddess incredibly early on. Insanely good buy and definitely worth investing.
Serrated Dirk
This item is a must-buy early for Senna if possible. It builds into a multitude of lethality items that you can choose from: Eclipse, Edge of Night, Youmuu's Ghostblade, The Collector, Serpent's Fang, Duskblade of Draktharr and Umbral Glaive.
Duskblade of Draktharr
Duskblade of Draktharr's passive has been updated so that it is now a must-have on most assassins. I think that it is a great item if you are snowballing on Senna support and for the most part remains a 4fun item. It is very situational, and because you can only buy one Mythic item now, its potential is immensely wasted and you would benefit significantly from different Mythics.
Serpent's Fang
After the buffs, Serpent's Fang is a remarkably strong item, especially vs champions with lots of shields like Janna or Lulu.
Eclipse is the most consistent Mythic item for Senna, I think that in most scenarios you should be buying it, unless you're going for Divine Sunderer or Moonstone Renewer.
Edge of Night
Edge of Night, is honestly severely underrated and a good kind of situational, making it a good buy whether you're behind or ahead. You get a fair amount of AD and lethality, but more importantly, the free spell shield that refreshes every 40 seconds. Because Senna doesn't have an escape, this could save your life from a deadly engage.
Black Cleaver
Because of the new build discovered in 10.11+, this item is viable and you basically have to buy it (if you're going Grasp). Outside of the Grasp build, you should not really buy this. If you ever buy this item, it will only because the enemy team is stacking armor, which, in that case, would make sense for you to buy Runaan's Hurricane to stack the passive much quicker.

- Stay Away
These are items that Senna cannot maximize the usage of or use them to her advantage completely. Some may work fine, others are items I'd advise you to not buy at all.

Spellthief's Edge
Spellthief's Edge is what most enchanter supports go. This is an alright start for Senna, but not good at all in the long run because she doesn't have much use for the ability power. In this case, Spectral Sickle is the superior option. The issue with Steel Shoulderguards is that Senna cannot really make use of the extra health gained. Moreover, it is easier for her to get the passive on Spellthief's Edge / Spectral Sickle. In difficult matchups where you cannot poke or are getting harassed easily, Steel Shoulderguards becomes viable then.
Since sheen items have all been converted to Mythics (with the exception of Lich Bane), Senna no longer should feel the need to buy any of the following.
Iceborn Gauntlet
Not worth investing here because you can get a very similar effect with Glacial Augment and its stats aren't that great for Senna.
Trinity Force
I don't think I need to explain why this is a bad buy, but I guess you could just go on and on.
Rapid Firecannon
I think that it is a waste on Senna support because it is costly, and you hardly benefit from building this item. It is viable if you decide to build Kraken Slayer and Guinsoo's Rageblade.
Youmuu's Ghostblade
Youmuu's Ghostblade, similarly to Duskblade of Draktharr, gives a decent amount of AD, 10% cooldown reduction and a nice active that grants you a boost of movement speed periodically, as well as a passive that gives you +40 out of combat movement speed. Building this early enables you to roam early while going back into lane without abandoning your ADC. I think that it has lost its touch in value and there are better lethality options.

I also have Senna's item set (11.3+) available at ! To use this, copy the text, click the "Collection" part of your league client, then to items, press "Import item sets" button, "paste a copied set", and paste it in the box that appears.
League of Legends Build Guide Author ayoshe
ayoshe Senna Guide
"First rule to being a sentinel...." S11.7

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Teamfight Tactics Guide