Undertale Last Breath
Last Breath is an alternative timeline of the Undertale game, where Gaster helps Sans in the main battle of the game. The support of Gaster brings health and stamina of the skeleton. The history of this timeline starts when the Human Child climbs on the Ebott mountain and then falls down, rolling right into the depth of the Underworld, where the demons live for ages. However, when they see the barbarian behavior of the Child, demons start wondering, who are the real monster here. Frisk start killing everyone he meets on his way, trying to dominate the reality and get the victory over the mightiest monsters. This nightmare made the creatures of Underworld shocked. However, there was someone watching from far away.
The routes of violence and genocide started and ended for ages. One day, monsters of the Underworld found a strange door and entered it. They saw a mysterious figure standing out there – it looked weak and broken. The creatures tried to communicate with the figure, but there was no reaction. Suddenly, it disappeared and the Human Child lost conscious. The invisible figure made his way to Snowdin and met Sans, the skeleton. The wise skeleton knows a lot about this world and can use telepathy to talk. Gaster (this is the name of the mysterious figure) finds Sans a suitable person for his plans. The skeleton is aware of the mass massacres and hard position of the monsters. Gaster didn’t have to convince Sans to help – he just shown the real feelings and emotions to the skeleton. At that moment, he decided to do everything and stop the Human Child. He will fight to the last breath and bring peace back to Underworld no matter what.
As you have already guessed, this timeline takes place when Frisk becomes violent and starts killing everyone in the Underworld. Sans supported by Gaster will stand against the child and the serious battle will start. Only the strongest will survive! Luckily, Sans has a powerful helper, who boosts his power and heals the wounds. Let this battle end happily – take part and bring Underworld to order again. Or make it drown in darkness forever.