Obzedat, Ultimate Collectors

When Obzedat, Ultimate Collectors enters the battle create a contract token. (They're artifacts with "At the beginning of each opponents upkeep that player may pay {3} and you sacrifice this permanent. If they do not they loose 1 life and you gain 1 life.)
Whenever a creature an opponent controls dies you may exile Obzedat, Ultimate Collectors. Return it to the battlefield under its owner's control at the beginning of your next upkeep. It gains haste.