Vivien, Monsters' Advocate (277)

You may look at the top card of your library any time.
You may cast creature spells from the top of your library.
: Create a 3/3 green Beast creature token. Put your choice of a vigilance counter, a reach counter, or a trample counter on it.
: When you next cast a creature spell this turn, search your library for a creature card with lesser mana value, put it onto the battlefield, then shuffle.