Mercadian Masques

When Mercadian Masques enter the battlefield.
Mask all creatures. (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. )
{u}{b}: Turn two target face-down creatures face
up. Destroy the creature with the lowest mana
value. Any player may activate this ability.
"Two Masqued Mercadian murderers meet, one
survives."