Ghroth, The Harbinger

Flying, Indestructible, Shroud
Ghroth, the Harbinger cannot attack.
When Ghroth, The Harbinger transforms, exile
the top 10 cards of each player's library. You
may play cards exiled this way and may use mana
as though it were mana of any color to cast spells
from among those cards.
Whenever you play a card from exile, you gain a Madness counter.
If you have 13 Madness counters, exile all
non-land permanents.