Pale or slightly bluish-skinned humanoid with the typical succubus/devil girl additions of horns, wings and tail. Only one specimen has been encountered so far. Her horns, wings and tail were very dark blue in colour, almost verging on black. As with other succubi, she was slightly taller than the average human woman and possessed a figure straight out of typical male fantasy—slender, toned and extremely busty.
Their identifying feature is a long black tongue terminating in a leech-like sucker mouth.
(Again I'm uncomfortable classifying the different variations of succubus as separate species. They could be, but they could also all be part of the same species, and the different feeding strategies and attack strategies we've observed could be the result of other factors such as exotic body augmentation and different training regimes.)
Only the primary feeding mechanism is known for this succubus. They feed using their long leech-like tongue. They use it to suck in a man's penis and then stimulate him to repeated ejaculations (usually with the help of mammary intercourse) until the man is fully depleted of fluids.
This happens rapidly, as fast as if the succubus was draining their blood. How do they induce the man to produce so much semen, so quickly? An agent in the saliva can't be enough. There must be some other factor.
As of yet we don't know anything about the offensive capabilities of this type of succubus. It's possible they are part of a civilian class and rely on other HSIOs such as the scarlet imps to bring them human captives. This is not an assumption I feel safe making. All succubi-class HSIOs encountered so far have shown formidable mind control skills and regenerative abilities. As always the best strategy is to disengage. If this is not possible, hit fast and hit hard before the mesmeric abilities of the succubus compromise your ability to fight them.
(Who am I kidding—High!)