Your opponent will likely want to defeat The Emperor [27-098L] before this ability can be activated
(However, you can only use the stamped rare or mythic rare promo in your sealed deck, not these special Prerelease promos.) These Prerelease promos can be found in non-foil and traditional foil, as can their planar Booster Fun versions: Approximately two thirds of Prerelease Packs contain a non-foil Prerelease promo
Terra, Magical Adept / Esper Terra Terra, Magical Adept, discounting the transformed side, is already a good 4/2 creature that mills and gives you a little value
The card is extremely cheap, however, and is at least inkable, so you can pop it in your inkwell if it's not going to make the difference
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