Nasus...
I don't understand how this champion is supposed to make a fun and creative game environment. All he does is stack 100% health/armor/MR while doing 300000 damage with a single Q because apparently it was a good idea to give his a stacking mechanic. Whether he get's fed or completely stomped on in lane, the outcome is always the same. He WILL stack, and he WILL 1 shot your carry, and he WILL destroy your entire base in a single minion wave. It's hilariously disgusting, and I'm not sure why this champion continues to have this play style.

Just two examples of counters.
they both actually have real counter play besides "win the game quickly". Sion only stacks health which is easy enough to counter with all the % health champions and items around. Veigar might have insane late game damage but is squishy and can easily be 1 shotted. Nasus on the other hand just forces you to send multiple people to fight him before he can 2-3 shot your turrets, which makes it really easy for the other members of Nasus's team to get another tower or Baron.