Rengar Sheen Bug
This bug/video was shared Months ago (although the bug itself existed long before that) and has yet to be addressed. With the current PBE changes (Statikk Shiv and Firecannon no longer stacking) I immediately thought to myself "Guess I'll be switching to Trinity Force" only to find that this bug STILL exists. I understand that Rengar is a frustrating champion to play against and fixing this bug will only buff him, but it's a bug nonetheless and needs to be fixed.
Note: This bug exists with All Sheen items, not just Trinity Force. Also note that Empowered Q doesn't receive the bonus damage of Sheen, regardless of whether or not it's the spell that charges the proc.