Um'Vrah, Sliver Ascended

+1: Add 1 mana of any color. If that mana is spent on a sliver, creature spell, it gains a +1/+1 counter.
-2: Search your library for a silver creature card. Reveal it and put it into your hand. Shuffle your library afterwards.
-8: Exile all non-sliver creatures. For each creature exiled this way, put a 1/1 colorless Sliver token into play under your control.