Welcome to my guide on Senna support.


I've tested Senna out on all lanes and found she can't solo lane and works best in support role.

more:
From trial and error I've found that because she doesn't gain ad per level and relies therefore heavily on her passive to keep up with other solo laners, she's just not strong enough to carry out the damage role.


RUNES:

Senna's Q ability procs on-hits (similarly to how Ezreal's Q works), which is why we go Glacial Augment for empowering Senna's long range Q and the Runaan's Hurricane to apply slows.

Free Boots - the best choice as Senna is ranged with now a slow, therefore not really needing a boots early purchase. Senna's slow aa speed makes boots almost completely un-impactful as an early purchase.

Biscuit Delivery - Senna benefits from aggressive trading which means you'll get low in lane and biscuits has the most value here to help allow you to do that and get a bunch of passive procs.

Approaching Velocity - guarantees you get in range for W and more aa's in fights and this overall helps with followup around your kit.

Font of Life - Having so many slows, this rune will make teamfights and skirmishes work better. E can be used to disengage and allow your adc or whoever is off-tank or on front line to gain lots of sustain.

Revitalize - Q guaranteeing procs, healing both aoe on your team and on yourself increased, and this rune will increase R shield size which is very helpful in late game.




ITEMS:
Unholy Grail - as a damage + cc with healing on a short cd (Q), this item is a must and very strong choice.
Hextech GLP - an easy to proc active synergizing with Glacial Augment that works in both losing and winning lanes. stats providing 20% cdr, mana, and ap.
Twin Shadows - another Glacial Augment synergy item. This will allow to have more opportunities for pics and teamfight impact on roams and a great mid-game item overall giving cdr as well
Runaan's Hurricane - the extra aa procs from the item will reduce the Q cd more, counting max for 3 aa per each one in fights or during wave clearing


Situational Items:
All situational items are to deal with different threats and comps and help your team crush comps that heavily rely on something

Early Game

Trade with Q+aa or aa+Q in order to gain ad procs early and use biscuit delivery to sustain through this aggressive laning style.
Standing behind the adc can be nice in order to be able to both proc Q's and heal adc during trades and skirmishes.
Stay in lane as much as possible in order to better farm passive from minion waves.


Mid Game

Abuse slowing actives and Q to catch out and harass enemies moving between lanes and to roam gank away from bot. If ahead, can head to mid w/ adc and create pressure, if not, can head top for some cheeky catches or just sit bot w/ adc and try to keep the tower alive.
Roaming with jg and invading can prove very powerful but try not to neglect lane passive farming.



Late Game

Stay in lanes as much as you can. You should never face check unless running around with scanner where you know they're not there in order to ward. Each wave in lane will now give you on average 3 stacks of passive, so it is a very good idea to stay grouped in whatever lane team wants to push and farm. Twin Shadows is a great way to engage, so is using E to confuse, surprise, or bait enemy teams into bad fights
Your aa range is very high now and should be north of 750. Use this to control the game and abuse your range.