The Guardians of Nature were released on the 26th of March 2010 as a part of the "Mod Mayhem" release. These dragons cannot be found in the Cave; they can only be obtained via the "Summon" breed specific action, available only when a user has on his/her scroll a complete Trio (Magma, Ice, and Thunder Dragon). This is because the strong powers of the Magma, Ice, and Thunder Dragons combine to summon the egg, giving it the great power to channel the forces of ice, fire and lightning. The Summon BSA also appears only when the scroll isn't locked from 4 eggs/hatchies, even if its cooldown (two weeks) is finished. There is rumored to be an 11% chance for a summoning to be successful. The Abandon action was removed for this dragon type because they are considered to be unique dragons for the Scroll Owner (see TJ09 IRC Chat comment below). There is a limit of two per scroll. Therefore, you can only have two successful summons and then the BSA will vanish and won't come back, so if you lose an egg/hatchling/dragon for some issues, you'll be never able to summon a third. This dragon is classified as rare (and is one of the rarest for the difficulty of obtain it) and even if it can have genders it currently has no breed specific action.
The inspiration for this breed comes from the Pokemon Lugia: a legend tells that it appears only when the Legendary Pokemons Zapdos (electric power), Moltres (fire power) and Articuno (ice power) combine their powers to summon it.
Cool huh?