Just take one champion and make a scenario where one of their abilities glitches in a weird way that would make people say WTF!? in game.
Here's an example:
uses her E and it hits the entire enemy team as they are lined up. The ability glitches and tries to make Leona dash to all of them at the same time. Leona suddenly splits into five Leona's, one for each enemy.
if lee sin teleports somewhere and tries to ward jump while the teleport is channeling he will fly to the ward after he teleports, so if he is teleporting bot lane and ward jumps to a ward in top lane he can fly across the entire map which allows him to cast abilities mid flight
so imagine taking the mid lane turret and all of a sudden, a lee sin flies past your screen and kicks you
If 
teleports somewhere, he can use his pull to take them with him. Such as the fountain.
Oh wait... http://youtu.be/NovYokP4s4g
Veigar's ult is 25% shorter due to a model error.
if vayne flashes in the way of condemn it hits her instead
When Draven's ult comes back to him, he takes damage.
's W dosn't go away, but the stun does. So he can litter the map and make crashes happen.
Solider wont do what Azir tells him to.Instead the solider makes fun of him all day with pigeon dances and noises.
After the Crescendo wears off the champions continue to dance and glide across the map while dancing.
Tibbers is accidentally replaced with the tibbers from doombots.
Uses flip near edge of map and throws them out of it for an instakill.
Permabans the user for selecting him.
If kalista dies while ulting the linked teammate they are stuck, untargetable and floating in the air
udyr recalls poppy dashes at him or something at last second he flies
If Skarner or Warwick ults a champion just as they are finishing a recall or teleport, he follows them to the place they are going, suppressing them as they arrive. Enjoy fountian, suckers!
More of a minor but interesting "glitch". If a champion ward-jumps to a stealth ward, that ward can then be seen by the enemy team for as long as it remains in play.
try this: lee sin in the back of ww and tristana in front of him lee sin and tristana are allies if lee sin and tris ult on ww together what will happen?which way will ww go? remember they are all on a line.
Zak dies in fountin, buy GA at the same time and get resurrected into 4 playable small blobs.
My W now polymorphs people into caster minions.
Her passive will pop on minion kills.
Voracity: Scoring a kill or assist Getting CS will reduce the cooldown of Katarina's abilities by 15 seconds.
