When Leonin Relic-Warder enters the battlefield, you may exile target artifact or enchantment. When Leonin Relic-Warder leaves the battlefield, return the exiled card to the battlefield under its owner's control.
Official Rulings for Leonin Relic-Warder
6/1/2011 : If Leonin Relic-Warder leaves the battlefield before its first ability has resolved, its second ability will trigger and when it resolves, do nothing. Then its first ability will resolve and exile the targeted artifact or enchantment with no way to return it to the battlefield.
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