Instant, U (1) As an additional cost to play Mask of the Mimic, sacrifice a creature. Search your library for a card with the same name as target nontoken creature and put that card into play. Then shuffle your library.1
Illus. Heather Hudson
You target a card in play which is a "Creature" or "Artifact Creature" card, even if that card is not currently a creature due to some effect. [D'Angelo 1999/06/01] Older cards of type Summon can also be targeted.
You can choose the sacrificed creature as the target, but if you do so the effect will fizzle on resolution and you will not get to look for a creature. [Duelist Magazine #25, Page 31]
You look for a card of the same name, the current type of the card does not matter. [WotC Rules Team 1998/03/18]
If a copy card, such as Clone, is targeted by this effect, you get to look for another copy of the card it is copying (not the Clone card). This is because a copy card actually takes on the name and initial characteristics of what it copies. [WotC Rules Team 1999/03/18]
You do not have to find a card if you do not want to. See Rule G19.4. [D'Angelo 2001/07/14]