Who is Senna?
Senna is Lucian’s wife. She became a Sentinel of light because the black mist that carries souls to the shadow Isles was drawn to her. So to help her be able to fight against it the Sentinel of Light took her in and trained her on how to channel her soul into a weapon of light. Lucian tried to save Senna from the curse and this is how he met Thresh; The Chain Warden. Lucian and Senna battled Thresh and during this battle, she was captured in his lantern.
Initial thoughts on Senna
She seems like a combination of a couple of characters already on League of Legends. She has attack familiarity of Jhin when it comes to the range of special moves and attack speed (the creator of Jhin did make her- Senior Champ Designer Riot August). She has a mix of Caitlyn because if she gets enough souls her range exceeds Caitlyn and Tristana because she has range scaling properties that enable her to increase her attack range. In addition, Seanna has properties of top-laners who can heal like Nasus, Yorick, Darius, etc. Finally, she has damage scaling champions like Veigar, Bard, and Nasus because the more souls she gets the more powerful she becomes
Senna Break Down
Senna Passive is called Absolution. When she attacks an enemy champion she applies a mist that lasts for 4 seconds. Senna’s next attack will collect the mist and deal bonus physical damage to that target. Now if enemy champions or minions or even monsters die near her there is a 1 and 5 chance a mist wraith will spawn; which she can destroy and absorb it. Absorbing the mist will increase her range, attack damage and crit chance over time. For every 20 stacks of mist, she gains 25 bonus range, 15% critical strike. Once she hits a 100 percent critical strike 35% converts to life steal.
Q: Piercing Darkness fires a bolt that heals allied champions and does damage to enemies. The cooldown of this is 15 seconds but if you attack with a basic attack you can decrease piercing darkness cooldown by one second. This is similar to Karma with her mantra.
W: Last Embrace: Seanna throws Black mist at you dealing physical damage and binds you. If a champion dies or minion it spreads out and roots nearby enemies for a few seconds.
E: Curse of the Black Mist: Active Senna surrounds herself with an aura of mist for a long duration. She gets a camouflage and she can give this to allies as well. If she uses a basic attack or ability she can be seen. She gets 20% bonus moving speed with this move.
R: Dawning Shadow: This is a global ultimate. She fires in a direction and fires a beam dealing physical damage to enemies. Those enemies will also be infected with mist. Keep in mind the damage comes from the center of the beam. The ult also shields allied champions for 3 seconds.
The Good About Senna
Riot billed her as support however I can see her being a universal champ. Meaning she can do any role.
Her ability to scale with souls and regain health with (Q) makes her a viable top.
Her ability to turn into a wraith (E) gives her movement speed which allows her the escape potential of a mid-laner and she has cc which (W)
She can use both the piercing darkness (Q) and last embrace (W) to JG.
She can take the role of ADC
She can take the role as support because her piecing darkness (Q) also heals champions and herself and her Dawning Shadow (R ) shields
The Bad About Senna
There is really no bad thing about this champion. Riot wants games to end fast. Based on this principle alone Seanna seems fair. She has a decent size mana pool starting at 350. She has poke, she scales, she has utility, she is a multi-lane champion. If the game goes beyond 30 minutes she will become a problem. I have seen players like Bunny Fu Fuu collect over a 120 plus mist which made his range 725 with rapid-fire cannon at 28 minutes. The bottom line is, the longer this game goes on the stronger she gets and that’s when she becomes a problem. I think this is the first champion Riot games got right out the gate.