IDK, it's basically a more expensive less reliable 7th drain life, or repeatable-ish hard CC for darkness.
7th?
My hands here are divided. On one hand, i like that it's not a 'deal x damage every turn' weapon, but on the other hand i feel it's a bit UP.
The 'Drain all
is i feel not much worth it when compared to the normal spell, which is much safer in the hand than waiting to be deflagged or something.
I suppose it's like Fahrenheit scaling-wise, but Fahrenheit doesn't drain quanta.
My suggestion is to make this drain life from a random target each turn and upgrade to non random targets. Or something like that.