Pretty sure this is bad because you can't get tempo back even though it's only 4 mana because you discard your threats. You aren't going to play cards like devilsaur egg to be good with this card when you fall behind. This is just terrible design really. Zoo doesn't want this either because they don't plan on winning from a lossed board. Even if you destroy a bunch of minions and tap and play a card it's not good. In control it could cost 8 mana a be about the same powerlevel. Really bad design plain and simple.
In other news this could single handedly put discard quest warlock on the map by completing the quest turn 4 and summoning the portal on 5.