A slugcat introduced in Rain World, specifically in its DLC known as Downpour, unlocked via solving a riddle left by the developers of the game.

"Chant His name upon 7 or 8 inscribed bricks of a pillar"
"His name can be found in the door of the desert"
"It does not matter whenever the door is opened, closed or passed through. The lock is the key and the key is the means."
"Do as you have done before, give it a name"

Inv's route is mostly a joke, making the game exceptionally harder, renaming locations to jokes, and ending their route off with a dating simulator. As such, Inv is not canon to the game's timeline.

Generally, they tend to either be referred to as "Inv" or "Enot", though other names for them exist as well.