From the Super Mario Wiki
Reachers are skeletal ghosts who inhabit the Sunken Ship in the game Super Mario RPG: Legend of the Seven Stars. They resemble large, sad, humanoid skeletons whose bodies are obscured by tombstones. Reachers attack by reaching towards a party member (hence the name) with their long skeletal arms. They can also attack by hurling a large bone (similar to Dry Bones) or by singing a haunting lullaby which will prevent a party member from using magic.
Like most powerful enemies in Super Mario RPG, only one Reacher will appear at a time in battle. Reachers are aided by other ghouls in combat like Greapers.
An unused enemy that appears in the game's programming seems to be a relative of a Reacher, but then with a blue chest. This look-a-like is known as Juju. It was stronger and had a better variety of special attacks such as Silver Bullet, and its Psychopath thought is 'K-9 is after my Bones!'.
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