Mavinda, Students' Advocate is a mythic Legendary Creature — Bird Advisor card from Strixhaven: School of Mages Promos (PSTX), collector number 21p. Current market price: $0.51 (foil $0.78), TCGplayer market prices via Scryfall.
Flying {0}: You may cast target instant or sorcery card from your graveyard this turn. If that spell doesn't target a creature you control, it costs {8} more to cast this way. If that spell would be put into your graveyard, exile it instead. Activate only once each turn. (You still pay the spell's costs. Timing rules for the spell still apply.)