Tereus of Twisted Truths

When Tereus of Twisted Truths enters the battlefield, exile all other nontoken creatures you control, then return them to the battlefield face down. While face down, they are colorless 2/2 creatures with "You may turn this card face up." and "{2}: Turn this card face up. This ability may be activated by any player."
Spells which target face-down creatures you control cost {x} more to cast, where X is the number of face-down creatures you control.