Prickly Dragon: Void + Plant
Magnet Dragon: Void + Earth
Blueflame Dragon: Void, Water, Fire
Aurora Dragon: Metal, Energy, Void
Toxic Dragon: Plant, Void, Energy
Storm Dragon: Energy, Wind, Void
Jelly Dragon: Void, Energy, Water
Dracula Dragon: Void, Metal, Wind
Swamp Dragon: Void, Earth, Plant
Alien Dragon: Void, Metal, Plant
Agent Dragon: Metal, Void, Earth
Prairie Dragon: Earth, Wind and Fire
Ash Dragon: Fire, Wind, Plant
Palm Dragon: Plant, Wind, Earth
Archangel Dragon; Earth, Fire, Wind, Water
Siren Dragon: Four Elements
Pixie Dragon: Four Elements
Narwhale Dragon: Four Elements
Dark Machine Dragon: Four Elements
Titan Dragon: Four Elements
Vortex Dragon: Four Elements
Planet Dragon: Four Elements
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Keep in mind also that for the last six dragons, the four elements are randomized as legendaries are their own type, not a combination of types. Post in the comments section when you find a combination for breeding that earns the legendary dragons. Also, if you are having trouble with a specific combination of elements, start switching the order of the dragons, or what hybrids you use in order to figure out which one contains the right mixture/formula.