Min was once a little boy living in the apartment building. During a game of hide and seek with his mom, he showed the first sign of monsterfication, a nosebleed. He transformed after seeing his mother get brutally killed by the Blind Monster. Rightfully traumatized by this event, his desire to not be found by any monster turns him into the Slime Monster
The Slime Monster takes the appearance of a translucent, anthropomorphic liquid with two human eyeballs floating where the head is. As the monster is mostly liquid in nature, it can slip through wherever liquids can reach. Unlike monsters, the Slime Monster is cowardly and prefers to runaway if it is spotted. If it is forced to fight, it will try to drown its target. It also can enter a corpse and use it like a puppet or costume.
Additionally, it appears capable of reason. Hyun Cha was able to make it realize some of its actions backfired on its desire not to be seen.
The children Hyun went to save see the monster dripping through the ceiling in their apartment. Later, when Hyun arrives, the monster has fully materialized. It is shocked that Hyun can see it and attempts to drown him. However, it notices a crack in the ceiling and uses it to flee instead.
After the criminals take over the apartment and execute someone, the Slime Monster uses her corpse as a disguise. However, as everyone else knows she is dead and was killed before totally monsterfying, the disguise fails. It exits the body and clings to the ceiling. Hyun manages to reason with it, but Joon Shin orders his men to incinerate it like every other monster they've encountered.