One of the most common i've seen, yet not a gamebreaking bug, is the White Glass Wings bug, they don't have any animation or following movements when attacking and they sit in mid air and detach from the player, now usually this kind of bug doesnt bother me in the slightest, but because a good 50%+ of players use WGW, it's so seeable and i think it gives me mild OCD XD
Anyways hope this is good, and good luck everyone!! =D