Tallyman's Abacus

When tallyman's abacus enters the battlefield,
create a 1/3 black Demon creature token.
{t}: Add {b} or {g}.
At the beginning of your end step, you may
group all creatures you control into seven piles
(piles can be empty). For each pile, if the total
power, total toughness, or total mana value of creatures in that pile is equal to seven, draw a
card.