The Incubator makes her appearance in the mysterious realm of Nowhere.
She is seen in all four ending routes, however, she is only fought in the Bad and Bad+ (non-canonical) endings, and is the final boss in these endings.
With Alessa Gillespie complete once again with her other half, Cheryl Mason, the Incubator forms and fuses with the God that has matured in her body, creating the image of a beautiful, angelic, dark-haired woman. She glows with a heavenly light and wears pristine white robes.
If Harry Mason failed to complete the Michael Kaufmann side quest earlier, then Kaufmann never appears. After the Incubator transforms, she immediately kills Dahlia Gillespie by lightning and immolation. Harry is forced to fight her and kill her. After the fight, Harry hears Cheryl's voice say "thank you" and "goodbye" and Incubator disappears.
If Harry Mason completed an earlier side quest to save Michael Kaufmann and find a vial of Aglaophotis, Kaufmann arrives and throws the Aglaophotis on the Incubator, expelling the evil from her body in the form of the Incubus, which Harry fights instead.
The Incubator reappears after the Incubus's death. Her aura dims and reveals Alessa, who gives Harry a newborn baby.
In the Good ending, she uses her power to save Harry and the baby by freezing the Otherworld as it collapses until Harry and the baby escape. She dies after the overuse of her powers, consumed by flames.
In the Good+ ending, she saves Harry, the baby and Cybil Bennett. She dies after the overuse of her powers, consumed by flames.
Despite her heavenly appearance, she seems to still be a monster, just like the Incubus.
The Incubator fights and behaves almost exactly like Incubus, except for the fact that it takes less damage to kill the Incubator. She is stationary and doesn't move, and a force field prevents Harry from being too close to her. She attacks by firing blasts of heavenly lightning in volleys of three. As she does a large amount of damage, it is advised to keep moving until she stops her volley and then attack with a high-strength firearm like the rifle.
It is possible to kill both Incubator and Incubus without dealing damage. If the player uses up all of Harry's ammunition before the fight and survives for a few minutes, the boss will react as if the final shot has been fired. However, this will not work if the player has the Hyper Blaster.
The name "Incubator" signifies an incubator for a premature baby - in this case, the "baby" is a demonic god, Incubus.
The Incubator is Alessa's mental image of God, which is much more saintly and "pure" in appearance than the Incubus, which also symbolizes Alessa's innocent ideals.
The Incubator also appears to be Alessa, only more adult-like.
The Incubator's death (as Alessa) in the Good and Good+ endings may be also considered similar to the death of the God in the myths of the Order: she died due to overuse of her powers.
- Incubator charges her lightning through her hands, so two lightning fields around her hands are seen before she strikes.
- In Silent Hill 3, Heather Mason has a God of Thunder outfit which may be a reference to Incubator. Among other tattoos, the outfit also adds square shaped tattoos on Heather's palms and her hair now has a grey-blue tint.