Marvo, Deep Operative

Veil of Time — Whenever this creature attacks, you may cast a spell with mana value X or less from your hand without paying its mana cost, where X is the number of attacking creatures.

Flash

Flying

When this creature enters, exile target spell an opponent controls.

Whenever this creature attacks, if a card is exiled with it, you may cast the exiled card without paying its mana cost.

Whenever The Seventh Doctor attacks, choose a card in your hand. Defending player guesses whether that card's mana value is greater than the number of artifacts you control. If they guessed wrong, you may cast it without paying its mana cost. If you don't cast a spell this way, investigate. (Create a Clue token. It's an artifact with ", Sacrifice this token: Draw a card.")

This spell costs less to cast for each different mana value among cards in your graveyard.

Whenever you discard a nonland card, you may cast it from your graveyard.

Flying

Whenever this creature attacks, mill four cards. You may cast an instant or sorcery spell from your graveyard with mana value 4 or less without paying its mana cost. If that spell would be put into your graveyard, exile it instead.

Whenever you cast your first spell each turn, reveal the top card of your library. You may cast it without paying its mana cost if it's a spell with lesser mana value. If you don't cast it, put it into your hand.