Full disclosure, inflation isn’t my thing, but you did get me wondering how it might play out in a game. Buried somewhere in the depths of uncalled methods in Yaffaif is the formula for hoop tension; basically what would be needed to work out the burst point. So I had thought about inflation as a feature, but not done anything with it.
What could the PC do if they became inflated? Most stories tend to stress the helplessness of the inflated character, which while it might press some people’s buttons, it’s not exactly a good trait for the protagonist in a game. It could be involuntary, something to be overcome to progress, but how to make it something positive - a possible solution to a puzzle? If the gas was lighter-than-air, then you might be able to float or fly over an obstacle, but flying is a problem; it basically breaks the usual mechanisms for constraining play and making other puzzles work - you could just float over them and skip, well, everything - it’s god-mode in a gas bottle. To make it useful as a mechanic in this way it has to be temporary; which I gather is of less appeal to the OP. Though I suppose you could make an inflation based flight sim, or a pool-toy battle royale (where being over inflated gave you more reach, but a higher risk of popping?). Perhaps a game where the PC can use there ability to inflate to bounce off obstacles - a platformer which turns physics simulator complete with the usual sharp spikes for the unwary? Perhaps the PC could take advantage of the compressed gas as an energy source propelling them about, or unleashing attacks - but that’s back to it having a very temporary effect. Though I could see some dark cartoon humour in Kerbal for inflated characters.
For NPCs its just as hard, inflation can be a status effect to disable enemies, but - temporary. Is there a way to make it useful as progression for a “friendly” NPC? Turn one into your personal blimp? Perhaps a path in a monstergirl/brother/slave owner sim? Or a path in a dating sim?
I’m struggling, probably because it isn’t my thing, to know what someone who was into it would like to play.