Nergui, Burgeonhorde Incarnate

When this creature first transforms into Nergui, Burgeonehorde Incarnate, mutate
onto it all creatures you control, then place +1/+1 counters onto it equal to the
combined power of those creatures.
Hexproof, haste.
{g/u}{u/r}{r/g}{t}: Put a creature mutated onto this creature into the battlefield.