Ideas for elevated difficulty and more complex mechanics: animal interactions, precipitation, water interactions, wind interactions, directional and variant lighting, mirrors, earthquakes, plant/fern/bryophyte interactions (volunteer plants, spreading plants, pop-ups, seasonal flowering, seed dropping), plants that respond to nutrient/sun/seasonal conditions, littering humans.

Mm, most of those sound like they would just add complexity, rather than fun. You find the optimal raking and then a squirrel RNG scampers across the grid? Fluid mechanics can be fun, but I have no idea how I would integrate them...

If you have ideas, you could try vibecoding them and see if they work. The page should be fully self-contained and have everything an agentic LLM could need.