The Sun Dragon is one of the three rare dragons, along side the Rainbow Dragon,and the Moon Dragon. The same as the Moon Dragon, the Sun Dragon must be bred with the Cold and Lightning elements. This can also be done many ways, the plain Cold+Lightning, the popular Fire+Storm, and then some others, Cold+Firefly/Scorch, Mountain+Sonic, the founder got his with Frost Fire + Lightning and the also popular Blue Fire+Crystal.
Many people say that the time that the dragons are bred can affect if it is a Sun Dragon or a Moon Dragon. For some people, it is that way (breed at night for Moon and day for Sun). But for other people, it's the exact opposite.