Dark Arts on Dark Passenger and Abyssal Drain appears to be broken

[Valonir]

If I said Darkside consumes around 200-300 MP and in combat you say you regenerate 138MP, with the amount of MP you say you loose with Darkside on during combat, do some maths. Or wait, I'll do it for you:

138+127=265 ---> Actual MP that Darkside takes away from you every tick, but because you regen MP in combat, it will only take 127MP, because you're adding 138MP to that 265MP loss.

Maths dude, they do wonders.

Please explain how you're figuring it consumes 200-300 MP. And just because 'oh 138+127 = 265 that's the mana cost because I said so' doesn't make it true, you can't actually tell because.. it doesn't show up in the combat log that you're regenerating mana.
Did you datamine this information, or do you just like throwing out maths for no reason?
It could very well shut off mana regen (which is more likely, considering it also is not affected by outside sources of mana regeneration) and just cost the flat 127 MP/tick.