A few small flaws may exist, but nothing super noticeable to the naked eye
Interestingly enough, if Ice Cauldron gets destroyed while it has a card attached to it, you can still play that card as though it were in your hand
Shutting down the ability of players to interact with the Urza opponent at instant speed is risky since you are merely shutting down their combo protection and not the combo itself
At that point, is it much better than Draining Whelk
(They attack each combat if able and attack a player other than you if able.) Whenever this creature attacks, it gets +X/+0 until end of turn, where X is the number of creatures you control
Excellent with any sacrifice strategy decks, like the new Juri, Master of the Revue or Mazirek, Kraul Death Priest