This was super fun!!! I really, really loved the concept of an engine builder game using armour stats. I also really liked that some of the better combos in the game (IMO) relied on debuffing yourself in some way. It was incredibly satisfying to find a powerful combo (I especially had this moment in the final fight where, after struggling at it for a while, I came up with a combo that let me absolutely steamroll the fight with a full health bar by the end). There are a lot of awesome little touches in the game like the helmets that stack up after each death, the damage numbers and particles during fights, and the accelerating time scale during fights which I thought added a lot of welcome suspense for some of my builds that revolved around healing or ramping damage. I also thought the concept behind the final fight was a creative way to cap off the game.
A few suggestions: I would consider maybe adding a bit more of a tutorial or hint text. I will say I kind of enjoyed just being thrown in and figuring it out as I went along - but there was a short bit before I figured out how to move the armour between the anvil/hearth/inventory. I liked the hearth and forced elemental upgrade mechanics but I found that I usually crippled myself with the lock mechanic - so I did not use it much. I think more ways to game the system and tailor your build, while still keeping the spirit of re-rolling and risking gambling away your better stats, would be sweet (usually if I rolled a bad build and way low on money I would just start the fight with the intention of losing so I could get my money refilled).
Overall, super fun game with an impressive amount of depth! Loved the sprites and sounds and main mechanic and all the little details! Well done!