The most effective way of breeding a scorch dragon is blue fire (lv 10 left) and a storm (lv 10 right). It has about a 20% success rate.
The egg is red with a turquoise lightning bolt. It takes 3 hours to breed, and another 3 hours to hatch. It can be purchased for 100 gems through the market. It gains you 2500 experience points when it hatches.
Other (slightly less effective) breeding methods include:
The firework dragon is a limited edition. It is only available during July of each year. It has a high success rate with several breeding combinations, so it is not too hard to get.
Some reported combinations:
The firework dragon takes 6 hours to breed, and another 6 hours to incubate. The egg is red, white, and blue with stars. It gives 12,500 XP upon hatching, and can be purchased for 704 gems in the market.
You have to breed a Earth and Metal Dragon. I have a Scoria Dragon and I bred it using a Earth and Metal Dragon. It may take a long time though.
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.
The easiest way to get firework dragon on Dragonvale is Earth + Blazing or Dodo + Blazing Good Luck!
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.
Earth Dragon and Cold Dragon