Doomsday Device

Doomsday Device has Hexproof as long as it's tapped.
{t}: Add {u} or {b} to your mana pool.
{4}{u}{b},{t}, Sacrafice a comon creature, exile Doomsday Device: Choose another target player. That player chooses another target player. Both chosen players exile all cards in their graveyards, exile their hands, exiles all noncomon cards they control, and exile the top 30 cards of their library. Activate only as a sorcery.