Okay guys I might not be the only one but I am annoyed I have hatched my collosus with a wraith about easily 10 times and only ONCE!!!!!!!!!!!!!! did I get any kind of a mix and it was a DeathWalker which I don't like I wanted Frost lord so please HOW DO I GET ONE D; sadness.
I so so so so so so relate to how annoyed and sad you are. I too have tried unsuccesfully many many times to mix pets. I have about 10 satyrs now, and many other unmixed baby pets. The only mixed pet I have is one ghast that mixed from one of the many wraith satyr attempts. The greatest sadness comes when someone I've hatched a pet with texts me to tell me how wonderful and great and stupendous their newly mixed pet is and how many wonderful talents it is revealing as they level it up and how generally awesome it is to have such a great mixed pet. I often wonder if there is something wrong with my characters or account that keeps mixing of pets at bay? I have done a lot of research and don't think that this can be but since I've been hatching pets since July of 2010 and have only one mixed pet to show for it I begin to have my doubts.
You aren't guaranteed a specific pet from a hatch, but to increase your chances you can try hatching with a frostlord and another hybrid like your darkwalker; since the hybrids don't mix you will have about a 50% chance of getting the one you want. I know it is frustrating, but when you get the pet you want it can be worth it. Good luck.