Look closer, it wasn't that hard to make. Just add a lot of lines tangled together and occasionally change the color/saturation. I kept the colors close to brown, green, dark yellow, and less saturated orange. There is a filled shape underneath to look more solid.
An example of what I wanted the plant monsters to look like. For @Hrothegar's Grass Knight game: https://scratch.mit.edu/projects/1233705652/ Which quality type is most fit to be used in the game? I could also add an outline to the higher quality drawings. Reference is from D&D but we could make something similar and call it something else.