Gragas vs Gangplank

Let Barrel Roll (Q) charge before detonating it: damage and slow grow the longer it sits on the ground, and if you don't recast it, it explodes on its own.

Drink Drunken Rage (W) before engaging: drinking takes 1 second, then you take less damage and your next auto hits every nearby enemy.

Engage with Body Slam (E) through a path without minions: you stop on the first enemy you meet, and hitting reduces its cooldown.

After Body Slam (E), cast Explosive Cask (R) behind your target: the blast knocks enemies away from the impact, sending them toward your team.

Destroy his kegs before he does: a Powder Keg (E) destroyed by an enemy is defused, and each keg loses health over time.

If you can engage, go all-in: his kit has no dash to escape.

If your team has several CCs, don't use them all at once: Remove Scurvy (W) cleanses all his CC, then has a 22 to 14 second cooldown.

In teamfights, get out of his kegs' area: each Powder Keg (E) explosion deals the damage of the attack that set it off, ignores part of your armor and slows you.