Theb, Theif of Keys

Flying, Haste
This creature costs {u} to cast equal to the number
of artifacts each opponent controls.
When theb, Theif of Keys enters the battlefield,
gain control of all artifacts. At the beginning of
your upkeep, each player may gain control of target
artifact they own.
Whenever a player loses control of an artifact they
own, Theb gets +3/+0 until end of turn.