I had thought of a new lethal mutation in cubs, which is being born with multiple tongues. A cub will be born with multiple tongues, which can cause difficulty in breathing due to blocking the airway (Sleep Apnea.) The mutation would give the cub severe cases of Sleep Apnea, making it difficult for the cub to breathe due to so many tongues blocking its airway. It would die after a few days or so due to this. The sleep apnea wouldn't be caused the same way like most, instead it would be blocking airways due to the multiple tongues overlapping, only connecting near the end down in the throat. The cub could wake up from time to time during the middle of the night, struggling to breathe.

This is my idea of what the overlapping tongues would look like and the posed artwork would look like (Sorry that it's poorly drawn.)
http://mm1.narvii.com/7683/25bae8f7100d51305f10e833bac66c948049350b776c8e1cr7-768-768_hq.jpg

I personally think that this would be a really interesting lethal idea, considering we dont have many lethal mutations. I'd really like to see something be done with this idea, although i'm not sure how often Lioden moderators check forums and posts. (I'll add onto this more later on if I come up with more ideas for this lethal idea.0