Viktor vs Kassadin

Poke with Hextech Ray (E), fired in the direction you choose: it hits every enemy in its line, and its upgrade adds an aftershock in its wake.

After Siphon Power (Q), land an auto within 4 seconds: it deals bonus magic damage, and the spell's shield covers you during the trade.

Place Gravity Field (W) in your target's path, then fire Hextech Ray (E): the field slows them, and if they stay in it for 1.25 seconds, they're stunned.

Glorious Evolution (passive) upgrades a spell every 100 Hex Fragments: Hextech Ray (E) to poke and clear, Siphon Power (Q) to survive, Gravity Field (W) to slow.

Place Arcane Storm (R) on grouped enemies: it follows the champions it just damaged on its own, and you can recast it to move it.

Take as many trades as you can before he hits level 6: without Riftwalk (R), he has no way to move quickly, to engage or to escape.

If you deal physical damage, lean on it in trades: Void Stone (passive) and Null Sphere (Q) only reduce magic damage.

When he recasts Riftwalk (R) back to back, back off and drag the teamfight out: each quick recast doubles its mana cost, and once he's out of mana he can't blink anymore.

Look to end the game early: at max rank, Riftwalk (R) only has a 2-second cooldown, and he blinks almost nonstop.