Ezreal vs Kog'Maw

Land Mystic Shot (Q) as often as you can: each hit lowers all your cooldowns and adds a Rising Spell Force (passive) stack.

Detonate Essence Flux (W) with a spell rather than an auto: the orb deals its damage either way, but a spell refunds its mana cost plus a bonus.

Save Arcane Shift (E) to escape unless the kill is certain: it's your only way to reposition, on a 26 to 14 second cooldown.

Cast Trueshot Barrage (R) across the map to finish a fleeing target: it hits everything in its line, but deals less to minions and non-epic monsters.

Engage when Bio-Arcane Barrage (W) ends: his attack range drops back to 500, and the spell has a 17-second cooldown.

If you can engage, go for him: with no dash or leap, Kog'Maw can only back off on foot, and Void Ooze (E) is his only slow.

Below 40% health, get out of range of Living Artillery (R): each shot then deals its max damage to you, and it reaches very far.

When he dies, move away from him: Icathian Surprise (passive) makes him explode 4 seconds later, dealing true damage to nearby enemies.