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.
There is no "marsh" dragon in dragonvale but if you are referring to the moss dragon the best way to get it is earth and plant, although you also have a chance to breed the tree dragon.