Bob-Munching Nephilim

Whenever an opponent casts a creature spell, create a 0/1 green Human creature token
named Bob.
Sacrifice a Bob: Choose one.
-Put a +1/+1 counter on Bob-Munching Nephilim.
-Add to your mana pool one mana of any color
in Bob-Munching Nephilim's color identity.

"Yumm!" -Last words heard by Bob.