The Dark Guardian

The Dark Guardian is a black stone-creature with red eyes which is easy to spot at any time of both day and night. It is twice the size of the Ancient Guardian and endures a lot more damage.

The Dark Guardian is an epic enemy that only makes an appearance once the player sacrifices the Ancient Petrified Heart on the Ancient Altar with the Ancient Ceremonial Dagger. Once spawned by the ritual, the Dark Guardian will appear right next to the altar. Therefore, the player need to be be extra careful.

When the player is close enough to the Dark Guardian, a scary and dark soundtrack will start playing.

Combat
When far enough from the player, it will throw dark boulders that work both as a shield (if the player is using a bow) and a weapon. It blocks arrows if hit by one, and damages the player sufficiently with each one. Once close enough, the Dark Guardian will start using his arm as his only melee option, and will do more damage than when in ranged.

To fight this beast, traps like "Thorn Tripwire" can be valuable to avoid close combat (Decrease movement speed) if the player is very deep within the Island. If the sea is close, luring the Dark Guardian down to the beach is another good way to avoid his melee attacks. The player can jump on a boat then from sufficient distance might fire towards it. Poison arrows will work a lot better in terms of doing damage over time.

It is recommended to stock up on White Flower Potion (instant Health) and bandages (Strong Bandage if possible).

Drops

 * Ancient Metal
 * Dark Guardian's Blood
 * Ancient Coin
 * Ancient Core
 * Ancient Flaming Eye Necklace (epic)
 * Ceremonial Mace of the Ancients (epic)

Source

 * Ancient Ceremonial Dagger
 * Ancient Petrified Heart
 * Ancient Altar
 * Ancient Guardian
 * Ancient Island

Trivia

 * If the player has more than one Ancient Petrified Heart and tries to spawn another Dark Guardian, the player will get the message "Now is not the time to sacrifice the heart". This means that the Ancient Guardians have been deactivated upon slaying the Dark Guardian, and will need to be reactivated again by using bombs to destroy ancient statues until the guardians reappear. It would seem to be around 3 or so statues until ancient guardians appear once more. Only when you hear the rumbling music that plays upon reaching an altar can you resummon another Dark Guardian.
 * Killing the Dark Guardian for the first time lets you complete the "Monster Hunter" Steam achievement.
 * The Heroic Dark Guardian is an even more dangerous version of this boss.