Gangplank vs Master Yi

Build a chain with Powder Keg (E): detonate the keg farthest from your opponent, and each keg whose area touches the previous one explodes too, all the way to them.

Last-hit minions and pop kegs with Parrrley (Q): a kill with the shot gives bonus gold, and so does a kill from a keg it sets off.

Save Remove Scurvy (W) for a key CC rather than for healing: it cleanses all CC on you, on a 22 to 14 second cooldown.

Cast Cannon Barrage (R) anywhere on the map to help a fight or cover an objective: each wave of cannonballs slows and damages in the area.

Against Highlander (R), don't run alone: regroup with your team, because he gains speed and ignores slows.

If you have CC other than a slow, land it right after Alpha Strike (Q): during the strike, he's untargetable, and Highlander (R) ignores slows.

If you have CC, interrupt Meditate (W): he channels it to heal, more at low health, and to reduce the damage he takes.

Put pressure on his jungle early on: Master Yi is strongest once he has his items, and each stolen camp delays him.