I honestly have no clue which player it was, but someone in this lobby was hacking the game to forcibly transform everyone.
I don't think it even gave them any sort of tactical advantage, it was just sorta funny.
This would legitimately be pretty fun as a gamemode. Something where you regularly transform into other characters throughout the match, either randomly, or maybe something like when you get a kill.
That being said that's 100% not in the game right now.