Riven Turnbull, Pact Binded

{t}: Add {b} or {u} to your mana pool. If a creature spell would be cast using this mana create two copies of that creature, and target opponent gains control and owns one of the copies. Except tokens created this way are not legendary.
When Riven Turnbull, Pact Binded leaves the battlefield exile all tokens created by Riven Turnbull, Pact Binded.