I just played a game as Amumu, and the Kat would ult and I would use my ult to stop it, and she would keep on ulting through my stun, and then continue after my stun wore off. We ended up losing the game because I couldn't stop her, so she would just ult in the middle of the team.
Amumu's ultimate isn't a stun. It is an type of CC called an Entangle.
An Entangle is essentially a snare which prevents the targets from autoattacking and snares do not stop channels.
If you want to stop channels as Amumu, you should save your stun (which is on your Q).
wow.. i didn't know this either... and I've been playing for 3 years...
An entangle is a root and a disarm combined. I'm pretty sure Amumu is the only champ with an entangle.
