Vandal Gragas Bug
There has been a bug with Vandal Gragas' animations for a very long time now, and despite being a well known and widely abused bug no action has been taken to get rid of it.
Here is how it works: whilst in the animation for the empowered auto attack from Gragas W, your Q and your R will have no casting animation - the projectile is still visible, but the champion model does not move - it stays in the W animation. The bug is 100% reproducible.
This can be used in numerous ways, but perhaps the most important is to hit opponents with skillshots they would otherwise dodge in lane (as they cannot see the windup and so have less time to react) by using empowered auto on a creep and then casting the spell targeting the enemy laner. This is especially effective for hitting an enemy that has a dash with your ultimate. I can recall (but not actually find, unfortunately) a clip of Panunu (famous AP Gragas main) abusing this bug to ult a Kassadin before he can react.
I'm a Gragas main, but this seriously needs to either be fixed or to have an official statement saying it's intended and it's okay to do.
Here is a clip of Panunu demonstrating the bug: https://www.youtube.com/watch?v=kmgLCzvZ6Os
Cheers.