Pilfering Niffler

When Pilfering Niffler enters the battlefield, you
gain control of each artifact you don't already
control.Whenever an artifact enters the battlefield,
if you don't control it, take control of it.
When Pilfering Niffler leaves the battlefield, each
player gains control of artifacts they own that you control.
Sacrifice an artifact: Pilfering Niffler gains indestructible until
end of turn.