When do you use Dark Passenger?

[JackFross]

Mana priority in single target is:

Dark Passenger - 884 mana for 150 potency ~0.17 pot/mp
DA+Carve and Spit - 2652 mana for +350 potency ~0.13 pot/mp*
DA+Souleater - 1768 mana for +120 potency ~0.07 pot/mp*

DA+CaS -
If you DON'T Dark Arts it, it's 100 Potency while restoring 884 Mana.
If you DO, it's 450 Potency with cost of 1768 Mana.
Difference is +350 Potency at a cost of 1768+884 = 2652 Mana, since you spend DA and no longer get the Mana regen.
Some people might argue I'm calculating this wrong, but I would disagree. The additional Mana healed from non-DA CaS is necessary when looking at the gains from pressing DA, because it's one charge - 50% of a DA elsewhere or an additional free shot of DP.
Saying the Mana isn't important to consider is saying "I would either DA+CaS or just never press CaS ever."

DA+Souleater -
If you aren't using DA+SE, you're using Delirium - 280 potency - NOT Souleater (260).
If you do DA+SE, it's 400 potency.
So you only gain +120, not +140 as several people have said here.


Fun fact:
On two targets, DA+DP is the single most efficient use of Mana you have for offensive power. You should shift a DA+SE into a DA+DP every time. Don't take a DA away from your CaS unless you have three or more enemies. At 3, the efficiency of DA+CaS equals DA+DP, but using regular CaS allows more shots of Unleash or Abyssal Drain, which are both net gains over base combos at that many mobs.


tl;dr: Dark Passenger should always be on cooldown. If it's not, you're leaving damage on the table.
And, talking strictly DPS: You should never be using DA+SE if your Mana will NOT be high enough before your DP or CaS comes off cooldown. You always want Mana to cast DP and to DA every CaS. DASE is significantly less efficient than either other mana option.