Nightmare Gottschalk is a central figure in the Wonderland series, introduced as a mysterious dream entity communicating solely with Alice in her dreams. He consistently appears with short silver hair, grey eyes, and extremely pale skin, his lips a near-purple hue from chronic poor health. A black-and-gold eyepatch perpetually covers his right eye, adhering to an unspecified rule. Outside dreams, he favors formal attire: a dark grey suit with a frilled white shirt, invariably featuring a purple handkerchief in the pocket.

His personality presents contradictions. Initially enigmatic and suspicious, he later reveals a childish, lazy, and selfish nature. He habitually evades responsibilities, especially his administrative duties as head of Clover Tower, by escaping into dreams or feigning illness. He possesses a significant sweet tooth, adores animals like cats and a baby seal named "Gomakichi," and openly eavesdrops on others' thoughts despite objections, frequently causing annoyance. Despite these flaws, he exhibits fierce loyalty and protectiveness toward those he cares about, expressing affection primarily through non-intimate cuddling; overt intimacy often causes him to become flustered or physically ill.

His powers are extensive and fearsome. As an incubus specializing in dreams, he wields absolute control within dreamscapes, manipulating environments and altering memories with precision—selectively erasing Alice's recollections of her sisters or past. He can levitate outside dreams and interact with parallel-world versions of himself, though this ability remains confined to dreams. He designed Blood Dupre's face to resemble Alice's ex-boyfriend, his motives undisclosed. He also induces headaches to suppress Alice's attempts to recall her past or question Peter White's familiarity.

Nightmare is not Wonderland's sole incubus. His surname "Gottschalk" translates to "god of mischief." He rejects being called a caterpillar, insisting he is a bagworm. Subordinates at Clover Tower genuinely respect him despite his ineffective leadership. While he claims indifference to gossip—even about himself—hints suggest otherwise. His dynamic with aide Gray Ringmarc involves constant friction over Nightmare's work avoidance and complaints about Gray's cooking, though he tolerates healthy food if prepared palatably.

Key elements include his vulnerability to haunted houses and his role in larger mysteries, such as facilitating Alice's arrival in Wonderland alongside Peter. His actions often serve to destabilize or protect Wonderland's equilibrium, leveraging his abilities to influence events directly and through proxies like Ace, whom he directs as a "chess piece."