Prepared is a mechanic from Secrets of Strixhaven on creatures that each have a spell attached. While a creature is prepared, you may cast a copy of its spell, which unprepares it. Some enter prepared, while others become prepared again when a condition is met.
Emeritus of Woe offers a copy of Demonic Tutor and prepares again whenever two or more creatures die in a turn. Harmonized Trio prepares a copy of Brainstorm by tapping creatures, and Grave Researcher can cast Reanimate once your graveyard holds three creature cards.
