Who am I, and why should you listen to me?

What is Senna good at?

THE PROS

Versatility: Senna is useful in a wide arrange of situations and can be picked without fear against many different types of botlanes and team compositions. Her itemization and runes also allow her to adapt to be able to survive and help the team under specific circumstances, making her decent even against some of her bad match-ups.

Power: Senna's kit allows her to carry the game and be independent of her ADC if they're not doing well. If you accidentally get a kill while trying to secure it, the money won't be wasted on you. Your passive also gives you some extra range, and if you keep stacking it you will be able to outrange literally every other champion in the game.

Scaling: Senna's passive allows her to scale indefinitely, meaning that as long as you keep landing your combos and grabbing your mist stacks from dead minions and monsters, you will continue to gain extra AD, crit chance and range. This turns Senna into a very useful champion that can stay in the game and bring utility and damage to the table even if the game is not on your favor.

Utility: All of her abilities can be used to her allies' advantage. She has a decent heal in her Q that scales very well and can end up meaning the difference between life or death for an ally, her W roots enemies allowing for easy picks, her E grants stealth and movement speed and her ultimate is not only a global damaging ability, but also a global shield.

THE CONS

Squishyness: If Senna gets CCd, there's not really much you can do to escape. Even though some of her builds can get around her squishyness, they do so by sacrificing part of her damage, which is one of her strong points.

Slow Auto-Attacks / low cooldowns: Your AAs are extremely slow for a pseudo-ADC. This means your item choices are heavily limited, as building any type of Attack Speed on Senna is basically losing money. Your cooldowns are also extremely long at the beginning, and you become very vulnerable while your abilities aren't active.

OK, but what does Senna do?

• Wraiths: Enemy units that die near Senna will spawn wraiths, pet NPCs that you can collect by auto-attacking them. Each of them grants 3 gold and 1 stack of mist, but they despawn after 8 seconds if Senna doesn't interact with them. Enemy champions and large monsters are guaranteed to spawn one of these upon death, while large minions are only guaranteed to drop them if Senna doesn't land the finishing blow on them. Similarly, there's a 22% droprate for regular minions which gets reduced to an 8.33% droprate if Senna lands the last hit on them. Epic monsters drop 2 wraths every time.
  
  
• Mist: Senna can also stack her passive by auto-attacking a champion twice in the span of 4 second. Upon hitting them the second time, you'll collect a stack of mist and you'll deal 1%-16% extra damage, based on the target's current health. This effect has a small cooldown as well. This is your main harassing tool in lane, and you should try to proc it as frequently as possible. Remember that hitting your Q also counts as an auto-attack, so you can very easily poke enemy champions hitting them with both in quick succession, which will also gran you a stack of mist.
  
  
• Absolution: Every stack of mist collected grants Senna 0.75 bonus attack damage. For every 20 stacks, Senna gains 25 bonus range and 15% critical strike chance. Once the crit chance exceeds 100%, she gains 35% of the excess as life steal instead. As a rule of thumb, you should try to collect 20 souls before the 7 minute mark, and after hitting that powerspike you can continue to scale into the late-game with ease. It's very important that you continue to stack your passive, because Senna does not gain AD with level, so you need to continuously collect mist to stay relevant.
  
  
• Relic Cannon: Senna's auto attacks deal 20% bonus attack damage and grant a percentage (10% at level 1, 15% at level 6, 20% at level 10) of the target's movement speed as bonus movement speed for 0.5 seconds after your attack hits. This is very useful when pursuing a target that's trying to escaper your range.

• Description: Senna fires a laser in the target direction, damaging any enemies by 40 / 70 / 100 / 130 / 160 (+ 40% bonus AD) and healing allies and herself by 40 / 60 / 80 / 100 / 120 (+ 40% bonus AD) (+ 25% AP). This ability also procs on-hit effects, including your passive.
  
  
• Usage: This is your main ability. The most important thing you need to know about it is that it is an auto attack reset, so you can cast it immediately after an auto attack to deal more damage in a short span of time, and even chaining it with another auto attack afterwards if the situation allows for it. This will allow you to outtrade most other supports and even some ADCs, and it's the optimal way to proc your passive to collect one extra stack of mist.
  
  
• Targetting: The targetting of this ability is a bit tricky, and may take a while to learn. The thing is, this ability actually has a bigger range than it allows you to target, so you will do damage to units that are outside of the targetting range. Use this to your advantage by targetting minions, towers, wards, your own allies or literally anything else that is targettable in the map to extend the range and hit enemies with it. One neat trick you can use for enemies that are out of range is to quickly set up a ward between you and your opponent, allowing you to target it and hit the enemy.

What runes should I take?

THE OPTIMAL RUNES:

Keystone: Glacial Augment This keystone is the one that works best for Senna, because it allows you to proc your passive much easily during laning phase to stack up on mist by using your AA+Q+AA combo. As we've already established, you need those stacks to scale, so the ability to slow enemies to hit them again before the timer on your passive runs out is invaluable for Senna. Your objective with Glacial Augment is to stack your passive as quickly and frequently as possible to try and outscale your opponent. You want to take this keystone against anything that isn't hard engage or tanks, as it gives you the highest damage output and helps you become more powerful in the late game. Take into account that you won't be able to survive being

Primary: Magical Footwear Senna doesn't really need to buy Boots early, so having Magical Footwear as your first primary rune is a smart money investment, as once you finish Umbral Glaive you'll only have to worry about buying your tier 2 boots.

Primary: Biscuit Delivery Senna's mana costs are painful to deal with in the early game, so we take Biscuit Delivery to mitigate those costs and ensure you can stay in lane longer. The health part of the item is okay, but you don't really need it considering you have a built-in self-heal in your Q. You can also buy the biscuits if you don't think you're going to need them, but I would keep them until level 6 or so just in case you need an extra mana boost.

Primary: Approach Velocity This rune has been recently changed, and now it synergizes even better with Senna's W. Approach Velocity will allow you to bully enemies that have been rooted much more easily, so take it against lanes in which you know you'll be able to make good use of it, like against immobile champions such as Taric or Miss Fortune.

Primary: Cosmic Insight You might prefer to take this over Approach Velocity because of the extra cooldown reduction. I take this rune if I know I won't get a chance to abuse the enemy botline too much, because on the long run it will be much more useful. It will also allow you to get free assists more frequently, since it reduces your ultimate's cooldown. If you use this rune, take it over Approach Velocity, as the other two primary runes are pretty much essential on Senna.

Secondary: Presence of Mind Even if the second rune from the Precision tree is flexible, you always want to take Presence of Mind on Senna, as it gives you a much needed mana boost. This rune works with both of Senna's runesets, so make sure you take it each and every time. Take into account that you will need to get a couple of takedowns early to make the best out of this runs.

Secondary: Cut Down Since Senna was the only marksman to not receive a health buff on patch 10.11, Cut Down has become much more useful for her recently. Make sure to focus whoever has the most health to make better use of this rune.

Secondary: Coup de Grace This rune can help you set up some kills, especially during laning phase. It's usually useful against tanky targets because it allows you to kill them easily, so it you're against a squishy lane wihout any healers you're probably better off getting Cut Down or Legend: Alacrity.

Secondary: Alacrity This is going to be the most controversial of my suggested secondary runes. I've already explained that I like to run an Attack Speed offensive rune on Senna, so you would think it would be enough, but in reality the other two Legend runes are not very useful on Senna ( Legend: Bloodline is not very effective because of your low attack speed and Legend: Tenacity won't save you from being deleted if you're CCd), and picking Legend: Alacrity actually helps to mitigate one of her weakest points: her attack speed. By no means does this mean this is the better rune on her, but I like to run it just to get an extra hits in during the late game. Take any of the other suggested runes if you don't feel comfortable with this.

THE EMERGENCY RUNES:

Keystone: Grasp of the Undying There has been a lot of discussion about this keystone. A lot of people thing it's OP and that it should be picked over Glacial Augment while other players state that it's not good at all and should never be considered. I'm somewhat in the middle of these, because even though I certainly believe it's overrated, it works very well when facing certain champions. It gives you a lot of extra health and defensive capabilities, allowing you to survive more and provide more utility while you're alive. You should pick Grasp of the Undying when against heavy engage and/or more than two assassins on the enemy team. Your objective here is not to harass and poke your enemy constantly, but to survive lane phase without feeding the enemy botlane. Keep in mind that you won't do nearly as much damage as with the other runeset because you won't be able to proc your passive nearly as much, but in exchange you'll be way tankier.

Primary: Font of Life None of the runes from the first row are very useful to Senna, so Font of Life is the one we want to take. It will give your ADC a tiny bit of extra sustain in lane, and it's certainly more useful than Demolish and Shield Bash on a long-ranged champion that only has a shield in her ultimate.

Primary: Bone Plating This rune will give you more survability during lane phase, and it will make it so champions who like to hook you like Pyke or Blitzcrank have a rougher time trying to get their ADC to kill you.

Primary: Revitalize Since we're aiming for survivability rather than pure tankiness with this rune page, Revitalize is our best option.