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
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
An 8/8 flying, vigilance, indestructible angel already demands an answer
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
For two mana, youre getting your choice of a 2/3 or a 1/2 and a 1/1 here