Crisper

The Crisper is an intangible spirit, similar to it's kin the Wisper both capable of passing through solid blocks. When provoked, they swell and shoot five balls of fire orbs from their mouth. These orbs linger on the surface they made contact with and can deal continuous fire damage to any creature that touches them. After firing, the Crisper begins chasing their target through terrain and solid objects in an attempt to deal contact damage. All attacks from the Crisper inflict the burn status which sets the player on fire and deals D.O.T.

Crispers are based off of Will-o'-wisps.

. Crisper is a unique monster found on any kind of Red Desert, Aether Sea, world and also in Icefire Forest mini-biomes. It is capturable.

Luna's Lab Notes
~ Can be useful as a pet as it's ability to phase through walls and illuminate an area with it's body and fire orbs can be a boon to deep excavation and mining expeditions. Additionally, the Crisper is immune to lava and as such, can be brought down to even the core of a planet with relative safety.

~ One of the few monsters in the entire game that does not end it's captured description with a period (".") Tisk tisk.

Source: 

https://github.com/sayterdarkwynd/FrackinUniverse/blob/master/monsters/ghosts/wisperish/crisper/crisper.monstertype