Arusi, Master Biomancer

The first spell you cast for it's mutate cost each
turn costs {2} less to cast.
{g/u}{g/u},{t}: Reveal the top four cards of your library
and exile a non-human creature card among
them, then put the rest on the bottom of your
library in any order. As long as that card remains exiled, it has mutate. It's mutate cost is equal to
it's mana cost.
You may cast creature cards from exile for
their mutate cost.