Ancient Dragon

The Ancient Dragon is an optional boss in Dark Souls II.

Description
The Ancient Dragon is an massive dragon that speaks telepathically to the player. It is completely neutral to the player until it is attacked a couple of times.

Speaking to the Ancient Dragon will give the player the Ashen Mist Heart, an object allowing the player to cross into the Memories of the Giants.

Location
The Dragon is found at the very top of the Dragon Shrine in a large, open arena past the Drakekeepers and Black Dragon Warriors.

Strategy
Going hand in hand with its size, the Ancient Dragon has a huge amount of health and will most likely one-shot the player with every attack unless the player has high flame defense or a very high stability shield. Its most dangerous and most common attack is when it flies up and breathes fire on to the floor covering a large area.

The startup for this attack is obvious however so, once you see the attack coming, run away. When it lands, stand somewhere in front of it to bait its straight forward fire breath which allows you to run towards the dragon and land a few hits.

Another strategy is staying near its tail, it gives a constant direction to run to and if the flames don't reach the player when they are at the end of it. It does however have a tail slam that does inflict a lot of damage but is easily avoided.

It is possible to become immune to its fire attacks by achieving 900 fire defense.

Summons may be targeted as they enter the fight, making it hard for the player to reliably summon two phantoms.

Summoning
Vengarl of Forossa can be summoned for this fight if his dialogue is exhausted in the Shaded Woods and his body killed. His summon sign is down the corridor towards the fog door.

Melinda the Butcher can also be summoned for this fight. Her summon sign is found just before the staircase to the boss.

Attacks
Flame Breath: A straight forward fire breath that sweeps from right to left.

Stomp: The Dragon attempts to stomp the player with its hind legs.

Bite: The Dragon will attempt to bite the player, sweeping from left to right.

Tail Slam: When the player is at the tip of the tail, the dragon will raise it's tail and slam it into the ground twice.

Flying Flame Breath: The Dragon will fly up and breath fire onto the arena covering a large area.

Inner Flame: If the player remains beneath the dragon, the dragon will look between it's forelegs and blow fire at the player.

Trivia

 * It's possible that the Dragon fought is a fake, or at least not the original Ancient Dragon, as it drops a Soul of a Giant upon death. It's very likely that the real Ancient Dragon is the Dragon Corpse hanging from the top of Freja's arena. (dialog from Nashandra and Shalquoir seems to imply this)
 * Ironically, to get the real Ancient Dragon soul, the player must talk to it and receive the Ashen Mist Heart. The player will then have to head to The Duke's Dear Freja's arena to enter the Dragon Memories area.