Good website for MLP CCG rules and stipulations: MLP CCG Wiki
Of the main 6 'powers' (Random, Studious, Stubborn, Inspired, Caretaker, Swift), not all - in fact, precious few - are stackable. :(
Swift, is (sort of) stackable (more like domino-effect)
Caretaker, is not stackable (thank God!)
but Studious? It just doesn't seem right or fair.
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The FIM Fiction blog (Apr. 18/14) speaks of this very same issue. (Read paragraphs 3 & 4).
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As much as I don't like sour grapes and normally don't endorse the idea of changing game rules, I seriously believe Studious should be stackable.