"Don't try to kill him, I know it's silly, but this Dummy is Immortal...” - Player looking at the Menacing Dummy (Ikaku suru yōna damī, 威嚇するようなダミー)

Summary:

The Menacing Dummy is the main training dummy NPCs in A Bizarre Day. They currently do not have any other purpose. They're located at the beach. These dummies are basically for training and can heal from them, or do an ice glitch where you hit multiple times IF they’re anchored. There is also a dummy similar to this dummy that you can speak to known as the Sentient Menacing Dummy with a light grey torso.

Appearance:

The Menacing Dummy dons a Tin Pot and has a permanent cold stare. It has white skin, jet-black trousers, and a coal-like shade of black for its torso.

Emanating from the center of it are several menacing (ゴゴゴゴ) particles, identical to the particles used for when a player poses.

Trivia:

The Menacing Dummy has unlimited health and cannot be killed.
There is a glitch where you can take some health out of the dummy, making it showing a health bar. But trying to "kill" it takes a while, due to its health.
The Menacing Dummy currently has no other purpose than to take hits as a training/ability testing mechanism. They are supposedly sentient, however, as they do breathe and one is even able to talk to the player. As a training dummy though, it has infinite health and can be moved around the map.
If you use the blood suck move via VTW/STW or literally any stand/spec with consumption or bloodsuck on a dummy, it will heal you. This could be useful for fights. This doesn't work with Santana.
The Menacing Dummy has menacing particles on it.
There is a glitch, where Menacing Dummy pieces scatter all over the map.
Attempting to make a D4C Bomb will not only fail with its name being D4CBomb it will immediately glitch and teleport off.
There is a glitch where dummies get ragdolled and ascend to the sky.
The dummy can be seen killed by exploits.