Certainly not Dolly!
Alexander knew full well that Dolly was a guardian in white, likely an adversary. To summon her now would be foolish.
These days, Alexander scarcely returns to the real world, let alone summon Dolly.
The secret weapon he spoke of is a one-time ghost skill obtained from a "Mist Instance"—Hell Curse!
Hell Curse
Tier: Special, One-time skill
Description: This is the ultimate spectral skill from a Ghost Emperor. Though the Emperor met his demise failing to break a curse on the 38th bus, this innate ability transformed into a peculiar energy, lying in wait for its fated owner.