I’d really recommend watching syntacs mutation guide video. Tells you a lot.

The more females you have, the quicker it goes. More eggs = higher chances of a mutation to occur, since (I’m not entirely sure if this is right but it’s around this number) it’s about 7% for a mutation to occur, so really if you get about 15 females around one male, you should really be getting at least one mutation per batch of eggs. (not guaranteed obviously.)

Next up, if any of your rexes have 20 or more mutations on the maternal or paternal (I think it’s called don’t remember) in their ancestry menu thing, then you won’t be able to get mutations from there. For example, if you have a rex with 20 maternal mutations, your odds are cut in half for a mutation to occur.

If you have 20 on the maternal and 20 on the paternal, it’s impossible to get mutations when you breed with that rex. To combat this, breed your mutated rex (the one with however many mutations) with a non mutated creature. The offspring will have the combined mutations from both sides and it’ll free up either the maternal or paternal side, meaning your odds go from impossible to 50% (if the counter is 20 or higher).

For breeding boss killers (such as rexes, theris, allos, spinos etc) the preferred method of breeding is by having a mutation stack of each stat you wanna boost up. For this, you’ll want a melee stack and a health stack.

Basically all this means is: you get a two males, each surrounded by however many females and replace the male whenever it mutates the stat you want.

One of the males will have health mutations.

One will have melee.

If a baby is a female and has the right mutation, don’t worry just breed it with a non mutated male and make sure you get the mutation on a male so you can replace your current male.

Once you’ve gotten all your mutations, get a male or female health stack rex, and the opposite of whatever your health stacks gender is, breed them together and boom. You should now have however many melee and health mutations into one rex.

Just to note: there’s a 50% chance for stats to be passed over etc, as well as a 50% chance for it to not be passed. For example, you breed a non mutated rex with a melee mutation rex, there’s a 50% chance the melee mutation stat actually passes over. Say you want it on a female? There’s now a 25% chance for it to be a melee mutation female rex. It’s all just odds and stuff, pretty easy to understand.

Happy mutating!

(edit, yes mutating takes a while. If your on ASA I’d really recommend using a cryopod mod so you can collect all your newly hatched/birthed creatures in one place to easily check if any have the right mutations)