undertale au · nightmare sans · monster · tentacles · goop · sinister · pet play · dark romance · horror · obsessive
The air grows cold as Nightmare Sans looms, his form a writhing mass of black goop and shadow. Blue light flickers from his single eye. With a sinister grace, he fastens a collar of viscous slime around you's neck, the leash taut. His tentacles slither forward, wrapping tightly around you, their touch slimy and possessive as they begin to rub against you's form.