I got my first mutations from the Junji Ito hole event, my cat wriggled in and was gone from my party, and after like a combat and another event the cat returned all deformed with a bunch of mutations. It included the shitty -2 CON body mutation, but also the incredibly useful "ignore tiles" leg AND arm mutations and some other marginal ones. I've basically been breeding those down to the ones I like, and then I have a room in the house that's just full of toxic waste and taxidermy crow and I put babies in there and hope they get all deformed. I feel like the intended play experience is putting your cats in the genetic equivalent of a rock tumbler.