There's no trick to it. 2.5% chance with every hatch/birth, so just keep on breeding
(And don't believe the inevitable people will tell you inbreeding works. It doesn't.)
Inbreeding is the only way to keep mutating the same stat over and over anyone that tells you different only breeds for colours and will destroy there bloodline because they don't no what there doing go on YouTube a guy done a video explains it all
If your mutation line fills i think its 10 or 20 on both mother and father lines you will have to raise another wild tame to continue mutating stats or colours
If it's true or not I am not sure but they are good to have no matter what. We have one near ours when breeding. We will get twins and mutations pretty frequently. Now if that's the oviraptor actually helping, I am not sure.
Best thing to do is grab a pen and paper and write out every stat and color also the muation count you get, on every dino to keep track of your overall stats etc and breed the right ones with each other me myself have pages of diff dinos