Morgana and Pantheon in ARURF
Brand used to be able to permanently stun someone by just spamming Q. If I recall, the latter was fixed pretty quickly with reduction to the stun length or something, and it's not an issue anymore after Brand's rework. Morg, however, just has to fish with Q and then keep the target permanently rooted with Q spam until it dies.
Pantheon isn't quite as bad as that, but still pretty bad: stun someone, it wears off, their attack against him is blocked by his passive, repeat. All while he spams Q for unavoidable damage. He largely ignores towers, too.
I get the feeling these champs should either be disabled for ARURF or at least get some ARURF-specific changes, because their enemies basically can't play the game.