Sun God Unification

Once each turn, when a Dragon God you control
attacks, you may exile the top card of your library
and if you do, the attacking creature gets +X/+X
equal to the exiled card's mana value.
At the beginning of the end step, shuffle up to
one Dragon God you control and all cards exiled
by Sun God's Unification into their owner's
library. If you do, gain life equal to that
Dragon God's power.