Board Thread:Dragon City Questions and Answers/@comment-41.129.86.37-20130520083623/@comment-10090661-20130828023439

By the way, the Crystal is in Difficulty group 3, which means you will have a better chance of getting it if the Pure Hybrids you are breeding are both level 4s or both high levels (Total Rate close to 50 or Total Rate approaching 1000).

It also helps if the other possibilities (Dragons) are few or limited.

If waiting for Breeding / Hatching is not your thing, then I'd probably suggest looking for combinations that produce fast breeding / hatching if you don't get a Legend. Unfortunately there is the matter of Pure Hybrids time being 42/48h. Can't do anything about that, sorry.