Nami vs Janna

Cast Aqua Prison (Q) on a slowed or immobile target, or where they're heading: the bubble lands in an area and stuns every enemy on impact.

Cast Tidecaller's Blessing (E) on your ADC just before they trade: their next autos and abilities slow and deal bonus magic damage.

Cast Ebb and Flow (W) so it bounces from one champion to another: it heals each ally, damages each enemy, and only hits the same champion once.

Cast Tidal Wave (R) to engage or to break an enemy engage: enemies hit take a knock-up and a slow, which lasts longer on those farther away.

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.