Sylass Ult
The problem with Sylass ult is that against every other champion you can plan your attack around the enemys ults in the teamfights. You cant plan or be prepared for Sylas because he can use any of your teams ult and you dont know for sure who hes going to pick. Against a malph or mumu you try to spread out so he cant stun everybody. Against a fiora or something you want to cluster and try to help burst her out before she can proc the vitals and kill your ally and heal her whole team. You never know what Sylas is gonna do.