When Piston Sledge enters the battlefield, attach it to target creature you control.
Equipped creature gets +3/+1.
Equip—Sacrifice an artifact.
If there are no creatures on the battlefield that Piston Sledge could be attached to when its enters-the-battlefield triggered ability resolves, it remains on the battlefield unattached.
You can sacrifice Piston Sledge to pay its own equip cost. It won’t become attached as it will be in your graveyard.