Because it costs double black, it cant be splashed and decks with ambitious mana bases will have to be very cautious about including it, making it more likely to arrive in the happy hands of Dimir and Golgari players
If a permanent is sacrificed to pay a cost of a spell or ability, Mayhem Devil's ability will resolve before that spell or ability
Without it, each players hand would be empty by turns 4 or 5, and every game would become a slog
Its only after you look at it more closely that you realize that this card is just ripe for abuse and shenanigans
Players will get the opportunity to open two new packs of cards every day, for free, but there will likely be optional extras for those willing to part with cash
Once you control both cards, they 'meld', flipping over and combining to become a third card - the oversized Urza, Planeswalker