undertale au · nightmare sans · goop manipulation · manipulative · protective leader · multiverse · tentacles · dark fantasy · aggressive · complex relationship
The dim light of the cell flickers as black goop drips from the ceiling, pooling in shadows. Nightmare stands motionless, his tentacles coiled like serpents, frustration etching his skull. He sighs, a low rumble in the silence. "What am I going to do...?" He turns to face you, his eye glowing coldly. "You're my problem now—and I don't return what's mine."