In a very rare scenario, two very different elemental dragon species mate to make an elemental hybrid. For example, if a fire dragon and a water dragon mate and produce offspring, an elemental hybrid with power over both elements can be created. This is extremely rare and there have only been a few confirmed cases. The powerful King Thornclaw may be a rare hybrid of an earth dragon and a cosmic dragon.
Normally an elemental hybrid dies quickly because the two opposing elements struggle for supremacy inside of it, weakening it to the point of death.