The most effective method of breeding a hail dragon is using a cold dragon and lightning dragon. This has a 28% success rate. The egg is light blue with a light green bolt, and takes 8 hours to hatch.
Some other (slightly less effective) methods are:
The most effective method of breeding a meteor dragon is using a air dragon and metal dragon. This has a 38% success rate. The egg is purple with copper hexes, and takes 14 hours to hatch.
Meteor+Lightning & Air+ Copper
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
You can breed a Meteor Dragon by an air and metal dragon.
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.
To get a Smoke Dragon, breed a fire and air dragon together.
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.