Now hear me out.

I know we have a lot of mutations in the works already, but these are ideas that could be easily implemented and made!

First Mutation - Psoriasis
For someone who has Psoriasis personally, i can attest to how annoying it is, even in small scales.
Psoriasis is a chronic disease and Its thought to be an immune system problem where infection-fighting cells attack healthy skin cells by mistake. Researchers believe that both genetics and environmental factors play a role. Now, I know it doesn't actually occur in felines, but, in the end, this is a game.
The mutation could show up as flakes and patches of dandruff appearing ontop of your lions lineart, as well as a special mutation-only skin-colour. Lions with this mutation could also have a stat penalty in Agility.

Second Mutation - Alopecia
A lot of people probably know what Alopecia is, but for those who don't, here's what google says.
"Alopecia areata is a disease that happens when the immune system attacks hair follicles and causes hair loss. Hair follicles are the structures in skin that form hair."
Lions who have this condition could potentially have bald spots and an excess amount of fur laying by their paws. This would require no lineart changes, simply adding another layer with the balding with the correlating skin-type.
Now, Alopecia is "curable". It can naturally heal itself, given the right conditions. I was thinking that perhaps if happiness and hunger is kept high and low respectively, there would be a chance at RO that it "heals". I.e that the mutation goes away. Granted, it would be a small chance, but still. Thought it might be cool.

Third Mutation - Chromhidrosis
Chromhidrosis is a condition that causes coloured sweat. I haven't been able to find any evidence of this occuring in felines, however, it is very rare and hard to notice. It's actually a condition caused from other compounds in ones body being released through sweat, but there might be evidence supporting that it occurs in people with "mutated" lymphnodes.
I'd say visually, it'd show a small puddle under the lions paws of one of the respective colours, as well as a tint on the nose. Chromhidrosis occurs in black, green, brown, yellow, or blue, but i could see it coming in other colours as well.

These are all the ideas i have for now, but i may return with others later! As i previously stated, i'll be updating this soon with examples!