The bone dragon is available around Halloween. Different combinations of the Earth Dragon and Fire Dragon are the most effective ways of getting a Bone Dragon. Fire (level 10 left) and Earth (level 10 right) seems to be the most effective method.
You can't breed a Bone Dragon after Halloween. To breed a Bone Dragon: Fire and Earth Dragon (level 10)
A bone and an invisible dragon
You can get in only in October. You can breed a Bone Dragon by a Fire and Earth Dragon. I have 2 Bone Dragons by that combination. You can buy a Bone Dragon for 25 gems.
You breed fire and earth dragons though sometimes you might get a lava dragon instead!!
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
you breed a ice dragon with a mine dragon
You have to breed a plant and a fire dragon.
As of July 2012, there has not been a star dragon in DragonVale.
You have to breed a sun and moon dragon together
You have to breed a metal and a water dragon together.
You have to breed a plasma dragon with a salamander dragon.
Breed the earth dragon with the fire dragon.