Arm With Darkness

As an additional cost to cast this spell, sacrifice a creature. Put X +1/+1 and a Menace counter on target creature, where X is equal to the sacrificed creature's power.
Deep in the wood the bones do rattle
A door slams down on prison gates
A hush falls over every battle
A seal falls over all your fates
-Becoming of Encirh, stanza 1