In DragonVale for the iPhone and iPad, the Leap Year is a limited dragon and is probably the rarest of all dragons now, since it’s only available every four years for just a few days on a leap year.
To get a Leap Year Dragon, you need to breed dragons together to toal four different attributes. For example, Love + Water will give you four basic attributes (lightning, plant, fire, and water). Be careful however, since some combinations won’t hatch for up to 36 hours, which may cause you to miss your limited window.
Check out my DragonVale Breeding Guide for more dragon breeding combinations.