Bro, imagine ghast!Tommy, he resides in the ribcage of his mother after she shed her last few years for him, to keep him hydrated, he's slowly dying, he can feel the heat drying his body to a crisp. But then, some traveler (could be Phil or Techno) finds him and takes pity on him. They take him back to their abode, before noticing the gills on the side of his neck, they place him in a tub of cool, refreshing water, and slowly, Tommy feels himself being revitalized.
I feel like ghast hybrids tend to grow rather large, so Tommy stays very, very small during his adolescent years, and then hits a major growth spurt during his teen years, towering over the people in his little family, even ranboo doesn't have anything on him.
Whoever took him in, would build a large pool just for Tommy, he may not necessarily need to be in the water to stay hydrated, but that doesn't mean he doesn't like the cool refreshed feeling he gets from it.
He also has a mean ass throw, and I mean it, his throwing strength is on another level. That doesn't mean he's very strong himself, but he can throw something pretty.