Monster evolution

A fascinating concept I encountered in some Japanese GameLit was monster evolution. The idea is that D&D monsters "evolve" (or more accurately metamorphose) into other monsters with increasing CR. This works similar to evolution in collectible monster games like Pokémon or Digimon. I suppose that technically this is metamorphosis, as evolution is a distinct scientific term.

The evolution is not necessarily a linear progression, but might branch into multiple different paths. The evolution might move in reverse, with higher CR monsters reverting to the form of lower CR monsters for whatever reason. Monsters might appear more or less humanoid as they evolve.

Evolution might form part of a life cycle a la metamorphosis, or it might be an independent indication of CR. Monsters might metamorphose into lower CR monsters as part of their life cycle, such as the tenebrous worm metamorphosing into the lower CR gloomwing.

GameLit seems to have plenty of examples. In That Time I Got Reincarnated as a Slime, goblins evolve into hobgoblins, ogres evolve into ogre mages, and orcs evolve into high orcs. In Overlord, skeleton mages evolve into elder liches evolve into overlords. In The Rising of the Shield Hero, some animals evolve into cute monster girls.

There are examples in mythology of dragons coming into existence this way: Fafnir the dwarf became a dragon due to cursed treasure, a koi fish who spent a century trying to jump the Dragon's Gate waterfall became a dragon, and the Korean imugi became a dragon after a fallen star granted their wish.

I enjoy the opportunities opened by the concept of monster evolution, as much or even more than that opened by spontaneous generation. I hope to be able to detail some more ideas in the future.