Two-headed threat
Two-headed dragons are a very rare mutation that results when two dragon eggs merge before being laid. The resulting egg is laid with much more magic energy than a regular egg. A two-headed dragon’s brains each have their own personality, which means it is hard for them to fly, given conflicts of interest. However, to make up for this and the added weight of an additional head, the shoulders are vastly more muscular thanthose of a regular dragon, and can deliver powerful blows. The dragon itself possesses unique magic capabilities due to using two magics. It is not uncommon for each head to use a magic that complements the other. For example, one head may spit pools of oil, and the other spits flames that ignite the oil around it. Along with dealing powerful blows, having two magics as a dragon makes atwo-headedd dragon a very powerful threat wherever encountered. As for drops, what would make a two-headed dragon a target for most players is the bonus of the drops having dual colors, as two-headed dragons have the scale colors of both the dragons that merged in the egg. For example, if the dragon has both teal and green scales, and it drops an armor, the armor will have teal as a primary color and green as a secondary color.
Reason to add two-headed dragons
Beyond the current confirmed dragon, I think realistically, mutations such as two-headed dragons, wingless dragons, and possibly other dragon species could exist out there in the world, especially in the dragon cluster.