Ekko's invisible grenade.

no

RITO's working on it XD, but I have yet to see one of these invisible projectiles. if they're playing a champ with range long enough to exploit it, chances are, you are too or your teammate didn't ping that say "mid is missing!"

ziggs can have a free kill from anywhere he wants to with his level 6 ult or force you into a fight against their team. Xerath does the same but with less efficiency and multiple targets, pantheon is always fun to "drop in" XD

the issues that annoy me are when you are outside of an AOE and still get hit, but it's minor, mostly having to do with lag and poor visuals

Edit: I do remember one, but I haven't seen one in a while and when they actually happen, it's nuts, but otherwise, not so much