Board Thread:Dragon City Questions and Answers/@comment-198.84.190.207-20130425213429/@comment-9946604-20130530183406

There are numerous posts explaining this very question. Please search the wiki before posting here again.

The basic idea:  You need to breed lightning and nature. Since you can't breed them directly, you need to include at least one hybrid that has one of those elements and either a hybrid containing the other or just the basic other.

Even then, this only gives you a CHANCE for a gummy. There are several other factors that effect this chance, such as the level of the parents and the generation of the parents. Check the breeding section for more info. Be mindful that it's in the process of a full overhaul.