Vivien, Monsters' Advocate
Legendary Planeswalker — Vivien
You may look at the top card of your library any time.
You may cast creature spells from the top of your library.
+1 : Create a 3/3 green Beast creature token. Put your choice of a vigilance counter, a reach counter, or a trample counter on it.
−2 : When you cast your next creature spell this turn, search your library for a creature card with lesser mana value, put it onto the battlefield, then shuffle.
If you cast a mutating creature spell, you must choose a target for it before the triggered ability from Vivien’s last ability puts a creature onto the battlefield. The creature you find can’t be the target of the mutating creature spell.