Sanstrocity

Sanstrocity is the third IT encountered in a creepy Snowdin,

Appearance
It's appearence consists on a smiling face in the center, with 2 small smiling mouths below and a bigger one, with even more smaller smiling mouths below. Outside of that, there's a circle of sans faces bones and eyes, with hands, feet, etc. poking out In sans circle and a ring google but this time with faster blasters faces.

Seperating
In the comic, You spare it by feeding it snow twice, then you use the locket.

In the fan-made unitale fight, It's pretty much the same method. his first few attacks are quite easy. after the first few attack he will begin to say some messed up dialogue. After you throw snow at it twice you can understand what he is saying

Killing
There seems to be no way to kill it, at least not in the fan made fight. It's possible, that you'd just have to run away, then fight it later in the last corridor, or at least sometime after P A P P Y