Senna vs Janna

Attack the souls held by the Mist whenever you can: each soul freed with Absolution (passive) increases your AD, attack range and crit chance.

Fire Piercing Darkness (Q) through an ally or an enemy to hit both: the beam heals your allies, and damages and slows enemies in the line.

Cast Last Embrace (W) on a target that's already slowed or immobilized: after a short delay, they and nearby enemies are rooted.

Cast Curse of the Black Mist (E) to engage or escape with your team: allies who enter it are camouflaged, then fast and unselectable.

Cast Dawning Shadow (R) to save an ally across the map: the beam has unlimited range and shields allies.

Avoid trading while her ally has Eye Of The Storm (E): the shield absorbs your damage and gives them AD.

Bait out Howling Gale (Q) or Monsoon (R) with a first engage, then re-engage right away: one has a 14-second cooldown, the other 130 to 100 seconds.

If you have CC, save it for Monsoon (R): after the knockback, she heals her allies as long as she stands still, and interrupting her cancels the heal.