Honestly a little surprised no one has done this yet
I've been tinkering around with the Origins mod for a while, and certainly enjoying my time with it singleplayer. However, the shortcomings and challenges of being some origins are cumbersome to manage (part of what makes it fun!) I've been considering making a multiplayer server for me and my friends, but I feel like just doing Origins would become stale fairly quickly. I've come to realize that the concept of starting with unique abilities, weaknesses, and environmental preferences is perfect for roleplaying as a Pixelmon!
The idea is fairly simple: You get a small selection of Pixelmon to start as, each with their own environmental abilities. By default, Levels don't vanish upon death anymore (inventory does, though). As you level up more as a Pixelmon, you gain new abilities. You can learn up to 4 abilities as per usual, and choose which of your old ones to replace. Some abilities are useful for surviving, some for battling, and some for exploring. Additionally, your Pixelmon origin can evolve under certain conditions, such as when holding an item in the offhand, or when at a certain level. Evolution improves your defense, attack, and opens the door for new abilities and/or changing of weaknesses. Evolving requires finding and being nearby a special block-entity to incite the event, so it isn't exactly free once you meet the requirement(s).
In short, think a Mystery Dungeon game, but Pixelmon and Minecraft! Ideally the mod fork would have the concepts I described, but just having Pixelmon-inspired abilities/weaknesses is just fine by my book. Pixelmon Origins just seems like a brilliant concept.