Monster Syumdang It has white fur and large ears like Syumdang, but its body is massive and grotesquely shaped with four arms. It mimics Syumdang's voice, and its eyes are completely black, including the sclera, with vertically slit pupils.

Monster Hyunsik It looks like Hyunsik, but only its face is black and wears a creepy smile. The body and ears are identical to Hyunsik's, but the face is as described above.

Monster Saedaegal He looks similar to the usual Saedaegal, but there's a sense of uncanny dissonance in his speech, memory, and personality. The whites of his eyes are red, and his memory is better than the original Saedaegal's. He lured the real-world Syumdang, Tangtang, Hyunsik, and Guest into the Backrooms.

Hyunsik A yellow Shiba Inu hybrid. He doesn't speak and communicates by writing on a handheld sign. He is terrified of needles. He has a foul mouth. He has beige hair. He was caught by Monster Hyunsik.

Tangtang A dark gray male cat hybrid. He has a rough way of speaking, using phrases like "Hey, you piece of sh*t!!" "Why are you doing this-tang?" "We're totally f*cked-tang..." "Suck my d*ck." "Stop talking bullsh*t." He has dark gray hair. He is trapped in the Backrooms.

Syumdang A white rat hybrid. Originally a lab rat used for illegal experiments, he escaped. Male. He is kinder and gentler than the other friends. However, he will curse when angry. His speech ends in "~syum" or "~syumdang," like "Something feels weird here-syumdang..." though he occasionally speaks clearly. He has white hair and a gentle appearance. He was likely caught by Monster Syumdang.

Saedaegal A pigeon hybrid. He has amnesia and can't even remember things from a minute ago. He's dim-witted, but if Tangtang smacks him on the head, he becomes smart for a moment before turning dumb again. He has gray hair and frequently says "Who are you-yong?" He ends his sentences with "~yong," like "Who are you-yong?" or "This is ruined-yong~" His current whereabouts are unknown.