Soulhoarder, Kevil

Kevil gains +1/+1 equal to your devotion to
black. (Each {b} in mana cost of creatures on
the battlefield under your control equal your
devotion to black.)
Eclipse {2} (Pay {2}, all black creatures gain +0/+2
until end of turn. If it was day, change it to night.)

This is one of the ones you want to fear most.