Defend Berk

Battle is a gamemode, It is available in the dropdown menu for quests if you have a minimum of 3 dragons at level 12.

Gamemode
The gamemode of Battle Mode has been shown in the trailer for the update. You can use dragons and ships to attack or defend Islands.

Release
Battle Mode was said to be coming around October, but needed more time. Battle Mode was finally released on December 02, 2014.

Dragons

 * Attacker Dragons (fire) deal high damage but have low health.
 * Defender Dragons (heart) deal low damage but have high health.
 * Sharpshooter Dragons (range) deal medium damage and have medium health but can attack from further away.
 * Dragons are better than the Catapult.

Catapult
The Catapult is a weapon used with your dragons when in Battle Mode.

Trivia

 * Toothless also has a Battle Mode Bar and can be used in the Raid Quests.