What if Sylas ult an enemy Slyas?

If Red Sylas attempts to use his ultimate on Blue Sylas it can go one of two ways.

If Blue Sylas doesn't have a copied ultimate prepared, Red Sylas will get message, similar to how Yasuo gets notified that "Enemies must be airborne" and nothing happens.

If Blue Sylas has copied an ultimate, Red Sylas will copy the same ultimate.

This could lead to you having a copy of a teammate's ultimate. Kind of cool actually.