In DragonVale for the Android & iOS devices (iPhone, iPad, etc.), the Ouroboros Dragon is rare dragon that is similar to the Apocalypse Dragon.
The Ouroboros Dragon has a base breeding time of 26 hours and 24 minutes, sells for 1,250,000 coins, and earns 250,000 XP for successful breeding once you reach level 17.
To breed a Ouroboros Dragon, you need to breed a dragon with a Magnetic element with a dragon that contains the Water element. Some popular combinations are Magnetic + Swamp, or Magnetic + Fog.
Check out my DragonVale Breeding Guide for more dragon breeding combinations in the game.
Need lots of gems at a cheap price? You can actually buy DragonVale gems on Ebay.