Fibrodysplasia is a disease that effects bones, making them weaker, causing fractures easily. Instead of healing like usual, fractures in those with this condition heal over with tough, bone-like scar tissue.
I've had this idea for a while (years now as of this edit!) and I think it could work in this game.
It would count as a "lethal" in rarity, and have some features that are similar, such as the cub dying due to the disease. However, these have a risk-reward type deal! They have a chance of surviving into adolescence or adulthood! However, they only have half, or less, of the average adult lifespan. (People with this condition live an average of 50 years)
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These are rough drafts for the possible art during the stages:
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"But Sweer!" some may ask, "What about game features relating to the different growth stages? Can the adols patrol or learn to hunt? Can the cubs train?"
Well, dear reader, it would work like this!!
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Cubs would not be able to train! Their bodies are too fragile and they would risk injury.
Adols would not be able to go on hunts or patrols.
Adults, if they made it that it, can't hunt, be kinged, or patrol! At this point in life they are way too stiff. However! If they're female, they can breed! They have a chance to pass their mutation (at a rate lower than other AMPs)! At a price. What price? THEIR LIVES! They have incredibly low fertilities, they risk losing some of the cubs, and they lose a few months (or more?) of their lifespan each litter they have.
You have to be sure not to give them hard items! Drones, coconuts, tortoise shells, they all are barred from these gnawable goodies!
--In the old version of this post, I had imagined that you could have them patrol, train, hunt, etc. at the cost of lifespan, however it's more streamlined to just have them barred from these activities--
= =========================Lethal Prompts ==========================

- 0 Months: Your lioness notices that Cub has a couple of short, bent toes. It suckles alright, so it should be okay,
- 1 Month: The Cub has had an unusual amount of swelling along its body.
- 2 Months: Cub got hurt while playing with the other cubs. Cub only tripped, but is mewling like a bone was broke...
- 3 Months: Cub's leg has healed in a strange position, twisted like a branch.
- 4 Months: Your lioness notices that Cub's swelling is back, but worse. The cub is mewling due to the bumps on its back..
- 5+ Months: Cub's body becomes more deformed over time
- 1 year: Cub's deformities have slowed. They are still at risk, regardless.
- Death: Lion has succumbed due to ossification of vital organs
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Health Messages:
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- [Cub] tripped over a stick and began to wail. Oh no. Another broken ankle.
- [Non-Mut Cub] stepped on [Cub's] tail on accident. They wouldn't stop apologizing, even as [Cub's} wailing started to drown them out.
- You bend down to lick [Cub's] back, barely rasping the poor cubs inflamed skin