Skull Kid, Possessed Imp

Flying
As long as an each opponent controls less than
four creatures, creatures your opponents control
get -1/-1.
"I went to great lengths to get that legendary mask.
When I finally had it... I could sense the doom of a
dark omen brewing... And now... that imp has it... I
am begging you! You must get that mask back quickly
or something horrible will happen!"
-The Happy Mask Salesman