Underdog (언더독, trailer) is a South Korean animated film from 2018, written and directed by Oh Sung-yoon at Odoltogi Studio, and co-directed by Lee Chun-baek who previously directed Leafie, A Hen into the Wild.
The main character is Moongchi, a dog who loves and trusts his owners, so he's understandably confused when he's deliberately left behind in the woods. Luckily he soon meets a group of other abandoned dogs who take him in, surviving in an empty slum on the edge of the nearby town.
While his fellow strays beg and scrounge to survive, Moongchi is still figuring things out. Wandering up the mountain into the forest, he meets a small group of wild dogs and wants to impress one of them, a female named Bami. Trouble is brewing for both groups, and soon they must unite and find a new place to live.