Sylas vs Kennen

Weave an auto after each spell: Petricite Burst (passive) turns it into a chain swing around you, with bonus magic damage.

Save Kingslayer (W) to finish or to save yourself when your health drops: its healing grows with your missing health.

To engage, cast Abscond (E), then recast within 3.5 seconds: Abduct (E) pulls you to the first enemy hit and knocks them into the air.

Cast Hijack (R) on the enemy whose ult can turn a teamfight: you keep a copy of it, cast with your own stats.

Dodge Thundering Shuriken (Q): each spell that hits you applies Mark of the Storm (passive), and on the third, you're stunned.

Back off as soon as he rushes at you with Lightning Rush (E): it's his engage, often followed by Slicing Maelstrom (R).

When he has Slicing Maelstrom (R), spread out from your allies: the storm hits every enemy around him, and its repeated hits end up stunning.

Wait for Slicing Maelstrom (R) to end before you fight back: during the storm, he gains armor and magic resist, then the spell has a 120-second cooldown.