I probably spent way too much time on something that will get ignored, but why not make a vendor for general items? Basically, you trade weight/size for a special currency, you use that currency at a vendor. And instead of conventional weapons, why not make them more trap-like? Or maybe be a tool or another item to trade?
The vendor could be a speaking entity, or it could be similar to the inter-dimensional vending machine (an SCP):
As for item ideas, there’s an artist on Deviantart that has A LOT of weight gain/inflation ideas; they could either be personal gadgets, or a way to remove enemies by laying out something temptingly inconspicuous yet discreetly debilitating:
- Fruit Themed
- Vegetable Themed
- Sugar Themed
- Even More Sugar Themed
- Animal Themed
- Video Game Themed
- Costume Themed
- And Even More Costumes
And that about sums up all the transformation lists they’ve made. There’s also a game on here called “The Inflation Rooms”, that might offer some ideas, like a machine where you can gamble your size:
And finally, there’s another Deviantartist who’s made a digital book on different inflation tropes in media (it costs money to get it, so it’s entirely up to you - I for one am planning on buying it):
https://www.deviantart.com/greyofpta/art/Inflation-Tropes-Is-Available-Now-946857893
Edit: Brief update, turns out that artist also has two more books, but they’re more specific to a sub-genre that might not be what you’re looking for:
Another Edit: Part of what inspired some of these was how you mentioned you wanted to involve puzzles in part of your game. Having some roundabout (no pun intended) ways to either inflate or further inflate some of the enemies into immobile forms or otherwise would probably help.
A reason for why guns could be excluded would probably be that either A.) some of these entities might still be humans that can be returned to normal/cured, B.) their skin is too tough to pop them, or C.) they’re never permanently popped (a good reason why some might respawn - I also just realized that an enemy that never stays permanently “gone” would probably be a bit terrifying).
And that’s about all I’ve got. Apologies if it’s too much for something that might not contribute much.