>>52831272The ideas that went into the forms is pretty easy to understand. Two unrelated Pokemon ended up looking like pre-existing ones due to evolutionary pressures or similar behaviors, which is exactly how convergent evolution happens in reality.
For the Wigglet line, it was an eel that developed a pronounced nose so it could better hide from it's predators like Veluza and Barraskewda. For the Toedscool line, it was a mushroom Pokemon that sprouted from the ground and started walking to better hunt prey by wrapping its mycelium around them and draining them of their fluids (which is similar to how the Tentacool line hunts, which is by wrapping them in their tentacles and stabbing them).
It's obviously to an exaggerated extent because no actual mushroom will just up and start walk, but Pokemon's been built on the extreme exaggeration of biological concepts mixed with standard sci-fi pseudoscience since Day 1.