Bard vs Xerath

Line up Cosmic Binding (Q) with a wall or a second enemy behind your target: the missile then stuns every enemy hit.

Cast Tempered Fate (R) to freeze a teamfight, or a tower during a dive: everything hit, allies included, goes into stasis.

Open Magical Journey (E) to roam or to get your team out: the portal crosses nearby terrain, but enemies can use it too.

Collect the Traveler's Call (passive) Chimes whenever your lane allows: they give XP and mana, and enough Chimes add area damage and a slow to your Meeps.

Keep minions between you and Xerath: Shocking Orb (E) stuns the first enemy hit, for longer the farther it has traveled.

Don't stand still, and change direction often: Arcanopulse (Q) hits a target moving forward or backward in a straight line much more easily.

If you can engage, go in while he charges Arcanopulse (Q): he slows down by up to 50%, and he has no dash to escape.

If you have CC and can reach him during Rite of the Arcane (R), use it: he channels the ult, and interrupting it stops his shots.