Wartale is an Undertale AU created by youtuber DuckWaffle on 30th August 2016 (Pacific time). It is an AU where the war between humans and monsters never ended and the monster created The Underground as a base of operations. Frisk stumbles apon The Underground accidentally and decides to try and end the war between humans and monsters.
Around the same time period of Undertale the monsters & humans are still locked in their war. Chara & Asriel had both died to the humans as Chara tried to stop the humans from killing Asriel leaving them both dead. Frisk then falls into the Underground and discovers the monsters living there. She decides to try and end the war by showing monster that not all humans are bad. Wartale has four endings (not including souless endings): Pacifist, Neutral, Genocide & Soldier. Neutral and Pacifist are the same as Undertale while in Genocide you kill Monsters and Humans & in the Soldier ending you kill only the leading monsters (bosses and mini-bosses).