Spree cards are a new level of flexibility as they are usually overcosted by design, but they are something you can sink a lot of mana into should you need to
Liliana's Contract Holy crap, is Liliana's Contract the best "you win the game" card ever printed
Magic: The Gathering gave this description for their Final Fantasy cards: MTG x Final Fantasy Summary Cast powerful spells, call upon classic summons, and visit your favorite locations on the back of a chocobo
River Song Our highest scoring Time Lord, red card and legendary dork is River Song, who I just built a Commander deck around earlier this week which you can find here
Delina, Wild Mage is one of the best, especially with cards that let you roll extra dice and pick the best for the result, potentially letting Delina copy a bunch of times on attack
With a haste enabler, like Lightning Greaves, and a way to untap creatures or generate mana on death, like Pitiless Plunderer, you can create an infinite loop of Joo Dees, filling your graveyard with the Surveil trigger