I have a few Ideas

Two Headed
i know they already exist but What I mean is when the lions Heads are separate (+Neck) that would make them able to survive. Maybe Not as Long as normal lions but at least a few years. This is Sort of a Variation to the two Headed cub. The Mutation would be able in both genders and would boost smarts. It can be breed without items but ist very rare and Offspring of this Mutation only has a 1% Chance of getting it.

Three legs
This would mean the Lion has two Front lege and one hind Leg. Since three-legged animals can be very fast, I suggest that they could have a Speed bist, but decreased strength. This Mutation can be breed but is unlikely to Pass on to the Offspring.

Deformed Heads
This would make the Lions head Look Like an Ugandan Knuckles. (If you don't know What that is, Google it) the Lion would die at 5 Months to 3 years die to breathing Problems. It can be bred but won't Pass onto the Offspring unless you give ist a Breeding Item.