this game is being made for everyone so I’m willing to put out 5 aspects into the game (which I think would be feasible in rpg maker vx ace) but I might pick more I might pick less, and no idea is too odd, so go right ahead and put your idea in, I’ll PM if I decide to put in that aspect
Aside from the obvious weight gain, perhaps, Macro, have the player able to become a giant if possible.
I’m curious to what kind of enemies will you have in your game, will they be some generic fantasy monsters? or like food themed?
well probably a combination of both, the only issue is that I’m not an artist so the food enemies wouldn’t be implemented until late into the development
I said this on the other RPG maker game, but perhaps implementing a “choose your gender and sexuality” option 
Like, playing as a gay dude
the only issue with that is that I’d feel uncomfortable writing that since I’m straight, I’ll consider it though
If you aren’t comfortable writing that part, maybe someone on the board would be willing to help with that part.
Specific Gain (increase to certain areas: butt, boobs, belly)
Lactation (though would also fall along the lines of BE)
the game will have overall weight gain, but some will have weight focus on the belly ass and boobs, it might not be what you ask for but it’s a demon that fattens not expands women
What about items like a fantasy-themed mobility scooter of some sort?
I could add that as a side quest minigame, but something like would only be implemented when I get a spriter