Underbird

Summary
Underbird is an Undertale AU made by Goosethehonker where humans and monsters were replaced with Cats and Birds

In the game, players control a kitty cat who has fallen into the Underground, a large, secluded region underneath the surface of the Earth, separated by a magic barrier. The player meets various birds during a quest to return to the surface, mainly through the combat system; the player navigates through mini-bullet hell attacks by the opponent, and can opt to pacify or subdue monsters in order to spare them instead of murdering them. These choices affect the game, with the dialogue, characters, and story changing based on outcomes.