Arcbound Overseer

At the beginning of your upkeep, put a +1/+1 counter on each creature you control with modular.
Modular 6 (This creature enters with six +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

The List

Darksteel

At the beginning of your upkeep, put a +1/+1 counter on each creature with modular you control.
Modular 6 (This comes into play with six +1/+1 counters on it. When it's put into a graveyard, you may put its +1/+1 counters on target artifact creature.)

If this creature gets enough -1/-1 counters put on it to cause its toughness to be 0 or less (or the damage marked on it to be lethal), modular will put a number of +1/+1 counters on the target artifact creature equal to the number of +1/+1 counters on this creature before it left the battlefield.