I have to say I think emperor is a decent addition to this game to enable possible card combos that couldn't be played because of the 10 mana limit. His power level needs to be addressed in the fact that he is a ticking time bomb and sometimes just one tick is enough to destroy the game. I understand that for value reasons most people would want his effect to work once dropped but on the other hand there is no counter play if you don't have a removal spell immediately you not only deal with the effect but also a 5/5.
Some solutions could be
1) not allow his effect to reduce cards cost a second time. Meaning only have it work on unaffected cards per turn.
2) make it a single use battle cry which could offer more strategic timing in playing the card to reduce for a next turn otk.
3) lower some of his stats but I don't think that's the big issue there. Putting him in range of 3dmg spells might make him to weak but he will still see play in combo decks.
4) add some kind of penalty to the player using him per effect proc.
Some solutions could be
1) not allow his effect to reduce cards cost a second time. Meaning only have it work on unaffected cards per turn.
2) make it a single use battle cry which could offer more strategic timing in playing the card to reduce for a next turn otk.
3) lower some of his stats but I don't think that's the big issue there. Putting him in range of 3dmg spells might make him to weak but he will still see play in combo decks.
4) add some kind of penalty to the player using him per effect proc.