I haven't really tried out arena mode so I can't say too much about it, but keep in mind that whatever your enemy can do - so can you. Pick a rogue and kill theirs before they get a chance to do anything.
With that being said one turn kills is probably not healthy for the longevity of the game mode and should be addressed in one way or the other.
your joking right? invis is the easiest thing to get rid of.. just use rain and anyone invisible will be immediately revealed.
With a source point as rogue you can teleport behind anyone and one-shot them in one turn.
Good luck casting rain during the opponent's turn.