So, I want to know how one would achieve a Deviant pet.

I'm not too sure. I think you can breed them though, because I got a deviant roc through breeding, and it wasn't even intended. 

From the FAQ:

"A baby born as homozygous (carrying two copies of the same gene) for color or pattern has a 1/10 chance to develop a deviant color when maturing.

This mutation is phenotypic and not inherited by the offsprings of an affected pet.
The color name of such pet gets asterisk (*) symbol to mark the deviation.

Deviant colors are available only through breeding. Wild pets can't have deviant colors."

As the FAQ says, you have a 1 in 10 chance to breed a deviant IF the parents both have the same colour, or pattern

For example. A dragon with piebald/piebald pattern that breeds with another piebald/pieblad patterened dragon will have a 10% chance of coming out as a deviant patterned dragon. 

Same goes for the colour! If its red/red and it breeds with another red/red then the offspring has a 1/10 chance to be a deviant ^^ Hope it helped 

(P.S. Only dragons, pumas, unicorns and rocs come in deviants patterns and colours. The rest do not (at least not yet)).