Exchange Market

{t}: Add {c}.
Sacrifice a Treasure, {4}: Mask Exchange Market
and target artifact or creature you do not control.
Exchange control of two target face down cards.
(To Mask a card, turn it face down. It becomes a
2/2 colorless creature. You may pay a masked card's
mana cost to turn it face up. Each player may then
rearrange their creatures as all other players look
away. )