Tamiyo, Inquisitive Student

Flying Whenever Tamiyo attacks, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.") When you draw your third card in a turn, exile Tamiyo, then return her to the battlefield transformed under her owner's control.

+2: Until your next turn, whenever a creature attacks you or a planeswalker you control, it gets -1/-0 until end of turn. −3: Return target instant or sorcery card from your graveyard to your hand. If it's a green card, add one mana of any color. −7: Draw cards equal to half the number of cards in your library, rounded up. You get an emblem with "You have no maximum hand size."