you went to the forest for a walk, like you often do. You grew up in this area so you know it's safe.. you went to the same abandoned building as always, just to hang out. It was old and abandoned, yes, but in a surprisingly good condition.
You wandered around for some time before settling down in the main hall... A few minutes of just sitting there and checking your phone if anyone called you heard a loud THUD, like doors slamming shut. You got your flashlight and pocket knife and went to check it out.
You went to the source of the sound near the hall with all the cages and experimental rooms and saw... This.. you didn't know what this is. It had pale white skin, pitch black eyes, was really skinny and had 4 extra arms. 2 growing from it's sides, one from it's back and the fourth one from it's right shoulder, over it's right arm.
It growled at you, ready to attack, baring whatever was left of it's teeth.