There are many mutations in this game, but I am honestly surprised than congenital hydrocephalus is not in the game. Same for polydactylism (but there is already a post for it so im not doing another one).

But back to hydrocephalus, you might know what this is because well its one of the most showed congenital abnormalities on the internet, but in case you don't know what it is it is a condition in which there is an accumulation of cerebrospinal fluid (CSF) within the brain. If its present at birth, the head will rapidly become larger and larger due to the bones of the skull not being fused yet.

Now Im not skilled enough do make a realistic drawing of a lion cub with this condition so here are pictures (WARNING: Might be disturbing for some viewers.)

http://www.ijaweb.org/articles/2012/56/5/images/IndianJAnaesth_2012_56_5_502_103979_u4.jpg
http://www.catster.com/wp-content/uploads/2015/08/ZekeMondayMiracle2.jpg

Now here the informations on the mutation:

Appears at: Birth
Lethal: Yes
Affects Gameplay: Yes

The reason it is lethal is fairly simple: In real life if the condition is left untreated the person or animal will most likely die from pressure on the brain. And in wild there is, or course, no treatment

I think there should be one different sprite for each rollover, the head of the cub becoming bigger each rollover because fluid accumulate in the brain. Until the cub dies when it stops growing (unless its too difficult to code, of course).

If this have been suggested before please tell me about it. And if you don't support, Id like to know why.
Thanks for reading

EDIT: WOOPS!! I noticed this was already suggested before. Though Im not going to delete this, instead I will copy-paste the link to the original suggestion so you can support or un-support it: https://www.lioden.com/topic.php?id=304429242430