I think it'd be really interesting to add some more hybrids to the game, specifically hybrids of lions and unusual/unnatural beings. A good example would be the nephelines in the current october event, angel-lion hybrids.
I think adding them in as event exclusive mutations could be really cool, maybe depending on who you side with you could be given the option to complete a challenge (similar to the punk challenge that guarantees you a dorsal fur cub) to breed one hybrid from your respective side (A nepheline if you side with heaven, a demonic lion for hell, a manticore if you dont choose a side) and the only way to get a special hybrid like that would be to complete the challenge or breed to one with the same rates as other hybrids (Or if not the challenge then trade in a lot of reputation or currency).

Theyd be a bit easier to get than other hybrids with yearly availability but I still think it'd be really cool to have them available for your pride! If making them rare or hard to get is a concern then maybe make them a bit more difficult to breed with low fertility or making them infertile so you have to use items, or maybe reverse the usual 'only female hybrids pass on the mutation' by making it so only Kings can pass on the event only mutation

The october specific ones are only an example, other monthly events could have other special mutations added as the devs see fit, obvs not every event is going to be able to have one but it'd be really cool to have a few that do!

TLDR: Hybrids are hella cool and I think mythical event only hybrids (like nepheline or maticores) would be a really cool mutation to add