Board Thread:Dragon City Questions and Answers/@comment-99.249.175.235-20130515225600/@comment-13460788-20130810111359

I am not sure, but I think that you would have a much better chance to get it by breeding mud(4lvl) and another mud(4lvl). The rate value would be 46, so that means that you would have 33.33% chance to get it. And it is not possible to get more %. The combination that you are using has rate value of 147, that means that the chance to get plankton is only 10%. There is more info here: http://dragoncity.wikia.com/wiki/Breeding/Rate_Value