Ceiling Surprise

The Ceiling Surprise is a white-pink ghost with a weird/creepy smile that always hides on the ceiling, and lowers down to scare Luigi when he's not looking at the ceiling. As the name implies, they are most likely to appear by surprise, which may scare the player if they're not expecting it. It is generally teamed up with Bowling Ghosts. Ceiling Surprises are extremely weak with zero HP, always drop a ten- or twenty-HP restoring heart when captured, and are the only ghosts in the game that cannot directly damage Luigi (this ghost can however, freeze Luigi temporarily making him vulnerable to other attacks from other ghosts such as bombs and bowling balls). The player may want to point the vacuum upwards for best suction results. It also goes away when sprayed by an element. But no matter what, Ceiling Surprises keep returning until the area is complete.

Purple Bomber
Purple Bombers are purple colored Ceiling Surprises and are usually found in the same places as them, but appear more often in later areas. One major difference between Ceiling Surprises and Purple Bombers is that, while Ceiling Surprises simply tend to be annoying, Purple Bombers can attack with dropping a little bomb. Confront the spook after the bomb explodes. Purple Bombers have zero heart points and can be sucked up without effort. Might want to point the nozzle up for best results when sucking the foe, or just spray with an element to make it leave. Unfortunately, it will come back as long as the area that Luigi is in is dark.

Trivia

 * The inspiration for the white Ceiling Surprise could be the Boo Blah.
 * The white Ceiling Surprises are the weakest ghosts in the game as they have 0 HP, possess no attacks and cannot hurt Luigi.
 * However, in the Bottom of the Well, if Luigi is outside the well and he goes back down and touches the Ceiling Surprise physically, then he will take damage.
 * If the player defeats a Ceiling Surprise (mostly white) with an element, it does not expel a heart.
 * It's possible that Nintendo put these ghosts in the game to cause a "jump scare" effect, not really to be a challenge for the player.
 * Both Ceiling Surprise and Purple Bomber will only appear if they get the chance of ambushing from behind.
 * Thus, if Luigi walks with his back to the wall whilst having the Poltergust 3000 active, they won't get this chance, leading to the result that they don't appear.