Introduction
Hi, my name is ShoDesu AKA J4NNA. I am a challenger support main that plays on the NA server and play Senna a decent amount on my main. If you have any questions that this guide does not cover, feel free to come to my stream and ask them! My twitch is https://twitch.tv/shodesu

Pros

+ Infinite Scale + Can solo carry + Counters most Enchanters + Global Ult + Unique support

Senna counters all enchanters and infintelty scales. She has a lot of presence on the map as her ult is global and she is one of the most unique supports as she can solo carry games.

Cons

- Hard to blind pick - Struggles against hook champs - No strong peeling abilities - Super Squishy

Senna does not fit into all team comps and has a lot of hard counters making her not blind pickable. You have to position very carefully as she does not have good peel abilities like most traditional enchanters.

Passive - Absolution When units die near Senna, their souls are periodically trapped by the Black Mist. Senna can attack these souls to free them, absorbing the Mist that held them in death. Mist fuels her Relic Cannon's power with increased Attack Damage, Attack Range, and Critical Strike Chance. Attacks from Senna's Relic Cannon take longer to fire, deal bonus damage, and briefly grant her a portion of her target's Move Speed.

Q - PIERCING DARKNESS From the twin barrels of her Relic Cannon, Senna fires a unified beam of light and shadow through a target, healing allies and damaging enemies.

W - LAST EMBRACE Senna sends forth a wave of Black Mist. If it hits an enemy it latches onto them hungrily, rooting them and everything nearby after a brief delay.

E - CURSE OF THE BLACK MIST Senna draws the Mist she has stored in her weapon into a storm around her, embracing darkness and becoming a wraith within. Allies who enter the area are camouflaged and also appear as wraiths as the Mist shrouds them. Wraiths gain increased Move Speed, are unselectable, and hide their identities.

R - DAWNING SHADOW Senna calls upon the relic stones of fallen Sentinels, splitting her relic cannon into a holy array of shadow and light. She then fires a global beam that shields allies from harm, while damaging enemies caught in the center.

FLEET FOOTWORK

VS

SUMMON AERY

Fleetfootwork provides Senna with more movement speed which I believe to be more valuable.

Aery provides more consitent damage/shields. I think the biggest trade off in both of these keystones are the runes in each tree. I believe the precision tree has a lot more runes that fit better with Senna's kit.

FLEET FOOTWORKI prefer to take Fleet Footwork because of the movement speed boost. Senna doesn't have a lot of GOOD peeling tools for when someone jumps on you, W is nice but it takes 1 second for it to trigger, E is nice but if an enemy is in your reach you will show.

Presence of Mind PoM is great for Senna because she has mana issues.

Legend: Alacrity Alacarity give attack speed which is nice for our lethality build, as most of the items dont give ANY attack speed.

Cut Down Cut down is great because Senna's base HP is super low and we dont build any HP items, so most champions will have more max health than you.

Magical Footwear Magical Footwear is nice because you're able to save 300 gold which will help you get your items quicker.

Jack of all trades Jack of all trades is amazing on Senna because you can easily get the 10 stacks from her items.

I will list out the tips and tricks on this section, but I go over in detail about them in my video which is less than 5 minutes.
Tip #1) Make sure to trade with auto q auto, rather than q auto auto. (you save time by animation canceling.
Tip #2) Look for Q snipes in lane. (use minions/wards to look for angles)
Tip #3) Make sure to be prepared for when souls drop out in laning phase. Grab them BEFORE they go too far.
Tip #4) In post-laning phase, make sure to follow junglers around their camps while pushing out waves to maximize farming and ganking potential.

Senna can have one of the most oppresive or weakest early games depending on the enemy support match up. Generally, you want to pick Senna into lanes where there is very little kill pressure (which is mostly going to be into enchanters) but if you're crazy enough to one trick her you'll most likely be playing into a lot of her counter match ups. Here are some tips for both MUs.

Enchanters
This match up is very easy for Senna becasue you out trade most enchanters due to Senna's q doing damage while healing and because of her auto's. Make sure you are walking up when you do have your Q up so you can win out on the trade. I think a big mistake a lot of Senna player's make is that they tend to use their heal a lot on their ADC in lane. There are sometimes when you need to heal them if they are super low, but most of the time you want to save Q to trade so you can not only win lane but to also stack a lot of souls. You should be playing super aggresively in this lane.

Hook Champs
This is by far Senna's worst match up because if you get hooked once you have to either blow summoners or you just die. You need to play super safe in this lane and you can only really walk up to trade when the enemy misses their abilities. It feels bad to play this conservatively but if you can make it out of laning phase even, you will outscale the enemy support. The most important thing about this match up is understanding this, that way you won't feel pressured to force trades and die. If you are running Fleet or Grasp, try to get q snipes on the enemy so you can heal more from your keystones.

After the tower falls and you swap over to midlane, you want to help secure the wave mid and then start moving with your jungler to optimize soul collecting. Each camp is guranteed to drop a soul so if you can rotate between lanes and jungle your souls will significantly increase. One of the best game plans is to push out mid, help your jungler take camps faster, and then play for the side you and your jungler end on. You not only have more souls but you increase the tempo for your jungler which can lead to first move into plays.

Senna has a lot of flexibiltiy for her builds as she can utilize a lot of keystones well. I have differents builds that I changed based on the draft and this is my flowchart for it. There are three keystones and variations of items for all the build except for enchanter. This flow chart might seem confusing at first but once you understand the process, itemization becomes a lot easier.

Build Overview

Enchanter

I build Senna enchanter if both comps are playing a front to back playstyle with a lot of front line. Even after her Q AP ratio was nerfed, I think Enchanter Senna is still strong. I don't have any variation for her enchanter build because I feel like this is the most optimal for her kit. Senna's enchanter scaling is compariable to Sona and you can become strong faster because of the gold you get from soles. Most people prefer the AD build because it feels better to carry with but I think enchanter is just as strong or stronger.

Grasp

Grasp is Senna's most popular keystone and I like running this into bot lane match ups where I am countered. It gives a lot more sustainability in lane as you have a lot more defensive runes. The reason why Grasp is so good on Senna is because you can trigger it with her Q from a safe distance and farming souls counts as combat. When you play around these two things, unplayable match ups become bearable as you can stack Grasp procs in lane. The main item for this build is Cleaver and depending on if you need anti-heal or anti-shield your build will change. I like to think of Grasp Senna as a debuff champion—essentially the opposite of an enchanter, where her main function is to serve as an armor-shredding, anti-shielding, and/or anti-healing unit. If you can understand that your job is less about doing damage and more about debuffing, this flow chart will make more sense.

Fleet

Fleet Senna's main function is dps. With her crit per 20 souls being buffed, I created this build to lean more into damage. You should always prioritize debuffing healing or shielding which is why this build gets split into two different bubbles.

In the case where you don't need to build either item, you can go a jack of all trades build where
you can actually solo carry a game. This build is very strong if you can get ahead as it is a nice mix of crit and lethality.

In the case where you do need to build either debuff item, we switch our secondary runes to not include jack of all trades as we wouldn't be able to make 10 unique stats. Every item from the fleet page has a replacement. if I need serpents, ill replace collector with it, if I need anti-heal, ill replace rfc for it.

The precision build feels the best when you can run jack of all trades. If your team has good anti-heal or anti-shield users you should ask your teammates to build those items instead of you. The most optimal anti-heal usage are any damage over time mages or control mages that build Liandries as the anti heal lasts for a long time. The most optimal anti-shield usage is any melee champion as melee champions apply a higher percentage of shield reduction. A lot of games in solo queue are lost because players get stat checked from heals/shields so its super important to know when you need them. Players are bad at itemization so its crucial to ask your teammates if they are going to get x debuff item(s) when your team needs it. A lot of the time they will not build it so you have to get it yourself.

If you want a more in-depth explanation for this flowchart, check out the video linked to the guide.

Senna is a fantastic champion that has a lot of skill expression not only from a micro standpoint but also from a build perspective. She is one of the most uniuqe champions that can adapt well into all kinds of drafts and if she is played well you can solo carry with her. It is hard to one trick her as she has a lot of bad matchups but if you can get past laning phase going even, you can take over a game. Senna gets a lot of hate in solo queue if you pick her as support so don't feel bad when players cry to switch off. Comp doesn't matter in solo queue until you get to the apex tiers of Grandmaster+.

https://www.youtube.com/ShoDesu Thank you!