Ancient Devil

The Ancient Devil (エインシェンデビル Ancient Devil) is an optional boss monster located and fought at the end of the optional Otka Island dungeon in. The Ancient Devil awaits players willing for a battling challenge and guards the summon tablet containing the Catastrophe summon sequence, basically fulfilling the same role the Sentinel did in Golden Sun: The Lost Age.

As a boss
The Ancient Devil is a level 46 enemy. It has no particular susceptibilities to status conditions. Its statistics are as follows:

The Ancient Devil acts twice per turn and uses the following battle commands with :

Defeating the Ancient Devil allows the player to access the Catastrophe summon.

Strategy
The Ancient Devil is one of the more challenging of the bonus bosses. A key aspect of this challenge lies in the Ancient Devil's unique ability to possess one of the player's Adepts. Possessed Adepts have access to any command they would normally access. Possessed Adepts seem to use a standard attack more than other options, but can also cast Psynergy and use any healing items in their inventory. More dangerously, they can use the player's standby Djinn to fuel summons against the player, even if the summon is an incompatible element.

When preparing to face the Ancient Devil, it is wise to assume that at least one Adept will be fighting against you for the entire battle. Thus, one option is to place more expendable Adepts in the front party, and to switch in key assets after Demon Sign has been used. By doing this, you can avoid the Ancient Devil possessing lethal characters such as Savage Fiend Sveta (which you JUST put into Beastform), or Master Matthew with mastered Sol Blade and 99% unleash chance, or highly useful characters like Pure Mage Rief. After a party member has been possessed, it is best to stick to single-target offenses as much as possible, to focus damage on the Ancient Devil. If the possessed party member is felled, they rejoin the reserve team in their KO'ed state, making them difficult to heal. In addition, the Ancient Devil can then possess another party member. The main exception is in cases where the Ancient Devil possesses a potentially lethal Adept.

Both Sveta and Matthew are excellent options for inflicting damage, due to both having access to powerful single target options in Beastform and the Sol Blade, respectively. If choosing to perform summons, plan on unleashing no more than a couple Djinn at a time, and summon that summon in the very same turn as the second Djinni being unleashed; otherwise, you run the risk of the summon being used against you. Keep in mind, however, that while summons will do proportionally less damage to the possessed Adept, they still may do enough damage to fell the Adept, triggering another Demon Sign. If you want to open with a powerful volley of summons, place your fastest characters in the front line and put enough Djinn On Standby in such a way that they can all be used in a single turn.

Barring Demon Sign, the Ancient Devil's other options are not truly devastating. Boosting Resistance should mitigate the damage done by Undead Might and Dire Inferno, while its Attack is not that damaging. Haures will be the most dangerous offense, due to the power and chance to inflict Deadly Venom. However, having a healer on hand should be enough to keep the party alive. The fight can be a long one (as it might be difficult to pull off powerful summons), but isn't overly difficult. It goes without saying that if a character is possessed when the boss is defeated, that character will receive no experience.

Background and story
The Ancient Devil, resembling a winged goat-like demon armed with a grimoire, does not have any bearing on the game's actual story, nor is any background information provided. It is a powerful entity standing guard within the deepest depths of Otka Island, in the unmapped dungeon section that can be accessed after the player has obtained the Sol Blade.

In the event any group of intrepid and capable Adepts discovers the secret dungeon and successfully traverse a long, skull-shaped maze, the Ancient Devil and the summon tablet await in a dark, torch-lit chamber at the end. The Ancient Devil will descend and introduce himself to the party before going on the offensive:


 * "I am the guardian of wind. Ye who desires more power must first reveal thine own."

Trivia

 * The Ancient Devil bears a striking resemblance to Baphomet.
 * In the game files, the Ancient Devil is named "Leonard", presumably a reference to Leonard, a demon in the Dictionnaire Infernal.
 * Coincidentally, all Psynergies cast by the Ancient Devil are accessible to Himi in her Curse Mage class. In fact, other than the Ancient Devil itself, she is the only person in Dark Dawn capable of casting Undead Might and Dire Inferno.