In Luigi’s Mansion 3 , the ball on the 13th floor (the Fitness Center) is a ghostly exercise ball used as a weapon during combat encounters with certain ghosts—especially the Hammer ghosts in the weight room.

What the ball does

  • Luigi can suck up the ball with the Poltergust.
  • He can then launch it at ghosts , stunning or “rendering them dizzy,” which makes them vulnerable to being vacuumed up.
  • It’s essentially part of the environmental combat mechanic in that floor’s gym setting—using fitness equipment as improvised weapons.

This is consistent with how Luigi’s Mansion 3 often turns floor-themed objects (bowling balls on the bowling floor, boxing gloves here, etc.) into tools for fighting ghosts.

Where you see it

You’ll mainly use the ball in the weight room section of 13F:

  • Two large red Hammer ghosts are working out: one boxing, one slamming weights.
  • After dealing with one, you’re expected to grab another ghost ball and fire it at the remaining ghost to finish the fight.

So the “ball on the 13th floor” isn’t a story item or key—it’s a combat道具 themed around the fitness center, designed to help you defeat tougher ghosts in that area. TL;DR: The ball on floor 13 is a ghostly exercise ball you suck up and shoot at Hammer ghosts to stun them so you can capture them.

Information gathered from public forums or data available on the internet and portrayed here.