Bat

Luigi's Mansion 1
A Bat is a minor type of ghost that first appears in Luigi's Mansion. They come in two different colors, violet (purple) and gold, and they often appear in enormous groups. Purple bats would hang upside-down from the ceiling. They can be found only in the hallways of the mansion, and when Luigi strolled past them, the mob of Bat spirits (purple) would fly downward to attack/damage the green-clad plumber. When they do this you can hear the flapping sound of their wings. If a bat managed to hit Luigi, the plumber would be slightly damaged (5 HP) and the poltergeist would disappear in a puff of dust. If the strike was failed and missed, the ghost Bat would return to the ceiling and prepare for the next attack. Gold Bats also hang upside-down on the ceiling. Note that unlike Purple Bats, Gold Bats would only attack if the player controlling Luigi pressed the "R" button while they're hanging upside-down on the ceiling. In all other respects, they were particularly the same as Violet Bats. These undead Bats could be easily sucked up with the Poltergust 3000 or immediately destroyed with elemental powers. They were not very dangerous to Luigi.

Luigi's Mansion 2
In Luigi's Mansion 2, they attack and do five HP damage to Luigi if they see him. They can be defeated by either sucking them in using the Poltergust 5000 or using the Strobulb on them. Using the Strobulb on them can make them drop a bill, a heart, or nothing. They can be hidden in furniture or windows after a curtain has been pulled. Gold Bats fly in a certain direction before disappearing; they are rarer than regular bats and yield twenty-five dollars when the Strobulb is used on them. Unlike their appearance in Luigi's Mansion, these variants are not ghosts.