Mad Dummy

The Mad Dummy is a monster that is a dummy that has been possessed by a ghost in the Underground.

Appearance
The Mad Dummy takes the appearance of a dummy with a set of upper teeth on the torso, a set of eyes on the head, and nostrils on the nose.

Personality
The Mad Dummy is shown to have a vengeful and aggressive personality, getting in the way of the player.

Pacifist/Neutral Route
When the Mad Dummy is encountered in the Garbage Dump in Waterfall, it reveals that the first dummy that you talked to was possessed by this dummy's cousin. No matter how you interacted with the first dummy, the Mad Dummy will be enraged by how you dealt with their cousin. It attacks the player with the intentions of stealing their soul.

In battle, the Fight command misses, the ACT commands do not impact the battle, and the opponent cannot be spared. As such, to defeat the Mad Dummy, the player must maneuver around the enemy's bullets so that they hit it instead of themselves.

Genocide Route
When encountering the Mad Dummy in the Genocide Route, the amount of hatred directed towards the player's actions allowed it to 'fuse with it's body'. It enters the player into battle, but instead of being named 'Mad Dummy', it is now named 'Glad Dummy'. This gives the player the option to spare it.

Trivia

 * The Mad Dummy makes several references to JoJo's Bizarre Adventure. He yells out "Feeble. Feeble! FEEBLE!", "Futile. Futile! FUTILE!", and "Pitiful. Pitiful! PITIFUL!" similar to how Dio Brando repeatedly yells out "MUDA MUDA MUDA!". He also pulls out a knife which can be alluded to how DIO in Stardust Crusaders pulls out and throws a multitude of knives.
 * It's also noteworthy to mention that the Dummy stands outside of Undyne's house because she changes color of your Soul green when you fight her. This may also be an allusion to the green hearts seen on DIO and his Stand, The World, in Stardust Crusaders.