I've been getting better at my own game to the point I realize on random runs I take little to no actual damage. Even going back to the game I am making a spiritual successor to and finding myself crushing it.

I have to ask; how do you properly balance your game if you're the only play tester for it? I tried the Mario idea of "switching hands of what they do" and that doesn't add much difficultly.

I'm using a Perlin noise gen so sure difficultly is inconsistent but still.

It's difficult because you can't really compensate for the skill that you acquired over the course of developing the game. Even if you stop playtesting and return a while later, you'll still be back up to speed rapidly. I'm not aware of too many methods to assess the difficulty of a game in a consistent manner.

I guess one way of doing so is to use a neural network to play through your game and determine how long it takes to converge (as a proxy for difficulty). But that also means you'll have to create a good enough neural network for the task, so it's a tossup - if you create an underpowered network then you might be misled into thinking the game is harder than it is.

Ultimately, proper game balance really happens with lots of people playing through it, and statistic being used to determine what to tweak by how much. At least it isn't multiplayer, or else that would be a whole other can of worms (that not even established companies have fully figured out yet)

Perhaps you could use seed-able random number generator and pre-make story/campaign levels.

Or you could make an AI that can play your game, then pre-run levels and make it play them first during loading. Then based off that experience tweak difficulty.

Though usually just making sure players can beat your game after multiple tries is good enough.

You can also balance every item/gun with some simple formula that seems to generally work.

Then also give game to friends for a playtest. Just ask them to look for fair/unfair parts. Or just to random people on Internet, maybe try to make sure they are also within age group you are targeting game for.