Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
At the beginning of your upkeep, you may move a +1/+1 counter from target creature onto Arcbound Fiend.
Modular 3 (This creature enters the battlefield with three +1/+1 counters on it. When it dies, 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.
The creature that’s targeted by Arcbound Fiend’s middle ability doesn’t have to have any +1/+1 counters on it. If it doesn’t have a counter on it when the ability resolves, nothing happens.