I'm curious -- why do you choose Darkness as the quanta for the skill? As evil as this may be, I don't necessarily think it has much to do with 'darkness' itself.
Let me think... manipulating the mind... through the use of singing...
Entropy likes to manipulate creatures (eg: mutation, butterfly effect, pandemonium, etc). Darkness, however... deals with being selfish (eg: taking what the opponent has [devourer, steal], strengthening yourself [eclipse, gargoyle, vampire, liquid shadow]).
More suitable if it costed 3 entropy, in my opinion. I haven't thought about possible advantages if it were in entropy -- neither darkness nor entropy go well with water.