One way to increase easily the difficulty & challenge of the game (without resources sliders for each resources type, that could be hard to code if all is well balanced/interdependent in the code, like discussed in the topic here : https://itch.io/t/851355/mewnbase-difficulty ) could be to have a simple "x2", "x3", (etc...) difficulty option for the recipes (doubling the necessary ingredients for a recipe, for the x2 option obviously!). Should be easy enough to code i think, and make a difference for the players searching for a challenge! (that way it increased the gameplay ever more, without deteriorating the relative balance of all things!)