That is wrong troll face first you must breed ice and ice with ice in ice habitat using ice engine in an ice world and in an ice island , it only costs a cheap 9 zillon millon billion kajillion killion Gems
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.
If you breed, say, a fluorescent and a firebird, the fluorescent has BOTH of the opposing elements of the firebird, so you probably have a higher chance of getting a rare hybrid. The dandelion + laser combo (how I got my gummy) could also produce a soccer or a cool-fire. Also try neon + nenufar/coral, star + jade/dragonfly, whatever has the two opposing elements of the other.