More info under the cut! If not, enjoy Gaster with large fangs.
So this Gaster wanted to try and recreate human souls, or something similar. So he and his team began gathering as many living things they could find that originated from the surface. This consisted of flowers, small animals that were thrown away like turtles and fish, and bats.
Surprisingly, the tiny bats worked best, making small, artificial souls. Supposedly.
Gaster, thinking that he had ended the monster’s problems forever, took the soul and attempted to fuse with it. However, Gaster’s soul completely absorbed the small soul, and no fusion occurred. Instead, Gaster was given Vampire-Bat like qualities and abilities, such as wings and large fangs. Even his Gaster Blaster’s changed to Vampire Bat skulls.
Despite these new changes, Gaster still works hard to come up with a solution.
TL;DR: Gaster fused with a Bat, now he’s a Vampire kinda.
Gaster needs to feed on blood. Doesn’t matter what kind. He usually asks hospitals or uses his own test subjects as a source of food.
Gaster can turn into a ‘Bat Gaster Blaster’ monster. He never, ever does this however.
He created Sans and Papyrus for test subjects, but instead adopted them as his sons.
Sans and Papyrus are his pride and joy. Sans got his intelligence and fondness of pranks, while Papyrus got his tall stature and love of puzzles.
Gaster is faintly aware of Alphys’ existence. She is San’s only friend.
Gaster occasionally uses Sans and Papyrus for harmless, fun tests.
He has a crush on Grillby. He did consider Asgore as a romantic partner, but figured it wouldn’t be a good time; since Toriel just left.
He needs to regularly feed or else his soul will start to break down.
His soul is very fragile.
While mostly harmless, he doesn’t always think of the test subject during his experiments.
