Dullahan

Dullahan is the strongest optional boss monster in both Golden Sun: The Lost Age and Golden Sun: Dark Dawn. In The Lost Age, it fought at the end of the optional dungeon Anemos Inner Sanctum, which can only be accessed in a Password-enhanced game where the player has amassed all 72 available Djinn in the GBA games. In Dark Dawn, on the other hand, it is fought in the post-game exclusive dungeon Crossbone Isle (an apparently separate incarnation of the Crossbone Isle featured in Golden Sun), which is accessible once the final boss of Dark Dawn has been defeated and a postgame save file has been created. In both games, the reward for defeating Dullahan is the Iris summon tablet, which is the "ultimate" summon.

As a boss in The Lost Age
The boss fight with Dullahan (who is level 50) at the end of Anemos Inner Sanctum automatically ensues the moment the player casts Hover on the glowing purple circular portion of a bird-like pattern that a puzzle requires arranging six white blocks to form.

Dullahan easily qualifies as the game's equivalent to many JRPGs' "optional superbosses", in that it is a much more deadly foe than any other individual enemy in the game, including the final boss. Put bluntly, this enemy cannot reasonably be expected to be fought successfully with a standard battling methodology, unless the party has been elevated to the highest possible level and is using an idealized class setup, because Dullahan regularly uses the abilities Formina Sage (an enormously powerful single-target attack), Charon (the second largest summon sequence in the game, which will both deal massive group damage to the battling party and likely instantly down an Adept or two with its side effect), and worst of all by far, Djinn Storm, which puts every Djinni on every currently-alive frontal party member into recovery mode. This erases a large fraction of the entire party's necessary statistics for a fairly long time, for only one Djinni will restore itself per turn, and it will take nine turns for all Djinn to return. Even if a party is developed enough that they could weather the proverbial storm of Dullahan's other powerful abilities on their own (which would actually not be all that hard assuming well-distributed healing and reviving measures like Pure Wish, Revive, and Water of Life across many party members), occurrences of Djinn Storm will mean that these other abilities can easily pick off severely weakened Adepts, and the lack of raised-class-stages will remove much of the party's access to the aforementioned Pure Wish and Revive Psynergies, as well as other potentially helpful options.

Granted, it is still entirely possible that a party that has been level-grinded into extremely high levels (with the help of the Wonder Birds at Islet Cave) and put into powerful classes - most popularly a setup where Isaac, Felix, Jenna, and Garet have all been placed into the Ronin class, which is both very durable and has access to a very powerful and consistent move in Quick Strike - can defeat Dullahan, assuming he never randomly selects Djinn Storm to essentially cripple half the group and turn them into sitting ducks (or at least only uses it when his HP has already been brought down to a fairly low level. At level 99, each Ronin can deal a Quick Strike amounting to 500 damage or more, and four Ronins can deal over 2000 damage a turn, which means Dullahan can be defeated in 7 or 8 turns.) But obviously, this is highly dependent on the luck factor that Djinn Storm introduces into what would otherwise be "just" a very damaging and stat-intensive battle. Most of Dullahan's other abilities are comparatively weak, and the fact Dullahan has so many such abilities helps reduce the likelihood of a Djinn Storm being fired off.

But in the much likelier scenario where the party's levels are around 50 or below, it simply becomes no longer quite viable to attempt to fight Dullahan traditionally at length, because Dullahan's abilities would likely be too powerful to contend with even if the party is lucky enough never to get hit by a Djinn Storm. Therefore, the most common method of battling Dullahan is to basically go into the battle with all eight Adepts having almost all of their Djinn On Standby, so that the extremely vulnerable Adepts use what little time they have alive to fire off as many high-powered Summons as possible. Summons will deal thousands of damage points because they deal additional damage proportional to how high the enemy's maximum HP rating is, and Dullahan has the highest HP in the game to begin with. Furthermore, summons deal the same damage regardless of the party's levels and are only affected by the party members' Elemental Power ratings, so the only method of making summons even more effective is wearing equipment that boosts elemental power, like the Feathered Robe, Big Bang Gloves, and Triton's Ward (though in general, Mercury-aligned summons will be the least effective because Dullahan's highest resistance is Mercury). This method essentially treats the battle as a coin flip, where the player is hoping that at least one of the second party's Adepts remain standing when Dullahan finally falls (and is also hoping that a Djinn Storm does not hit the current party before the current party can use all of their Djinn for summoning), and the player simply reloads the game file when defeated and tries this approach again until their victory.

One of the most important ingredients in raising the chance that this Summon-rushing approach against Dullahan will be a success is that the party's Agility ratings are high; Dullahan has 241 Agility, so each surviving party member that has more than 241 agility will be assured their chance to fire off a Summon against him at the start of the turn, while each party member close to the 241 agility mark will at least be able to take their action before Dullahan's second and third actions for the turn. Therefore, Quick Boots, Running Shirt, Feathered Robe, Wild Coat, and various other pieces of gear that raise Agility can be more useful to use for this battle than equipment that increases power or survivability. If Agility is a particular problem for the party, Moloch can be used as one of the mass of summons being unleashed against Dullahan, for its side effect will halve Dullahan's agility for several turns (note that this agility-halving will only start coming into effect on the following turn).

Assuming that each Adept only has Djinn matching their element, there are several established setups for both the front and back parties that allow party members to try to summon all they can in the most efficient manner:
 * One party has both Venus Adepts and both Jupiter Adepts, allowing them to summon Charon twice and Thor multiple times, while the other party has both Mars Adepts and both Mercury Adepts, allowing them to summon Ulysses many times.
 * One party has both Venus Adepts and both Mars Adepts, allowing them to summon Daedalus and others, while the other party has both Jupiter Adepts and both Mercury Adepts, allowing them to repeatedly summon Eclipse.

In a rarer setup, if every frontal party member's Agility rating is higher than Dullahan's even without there being Djinn Set to increase each of their class stages, then the Jupiter Djinni Lull can effectively allow an entire free turn worth of summons against Dullahan for the first turn of battle. If the party member with the lowest Agility rating among this super-fast group has Lull Set onto him/her while most or all of his/her Djinn are on Standby, then after each of the other three faster party members perform their summons, the fourth member can use Lull to end the turn before Dullahan can perform any of his own moves. Then, for the second turn, since all four of the party members will assuredly be both untouched and be able to act before Dullahan's actions that turn, they will all be able to deliver another full-powered round of summons. Remember that a party member that performs a summon receives a large temporary boost to their Elemental Power rating, which will cause another summon performed by the same Adept to be even more powerful than it would have been the first turn. Depending on the setup of the party, which summons each Adept is allowed to use, and which pieces of Elemental Power-increasing equipment the Adepts can wear, it is possible to have Dullahan defeated by the second turn, before Dullahan can execute a single battle command.

Note that in the Hard Mode, Dullahan does not receive as large a boost to his difficulty as other enemies because there is a hard cap of 16,383 HP on enemies in The Lost Age, so Dullahan's 16,000 base HP will only gain 383 HP extra. However, the boost to his Attack statistic and Defense statistics will not be inhibited, which will cause his Formina Sage attacks to be all the more likely to down an Adept in one hit, and will cause physically-aligned attacks used against him to be somewhat lower in damage output.

Dullahan's statistics are as follows

Dullahan regenerates 200 HP and 100 PP at the end of every turn, effectively granting him infinite PP.

Dullahan uses these battle commands:

As a boss in Dark Dawn
The boss fight with this version of Dullahan (who is level 48) takes place at the end of the deepest floor of the Dark Dawn incarnation of Crossbone Isle, ensuing once you approach the Iris summon tablet (at first, the six blue torches in the room will light out as though to provide the player with an opportunity to turn back, and then taking a step further toward the tablet will make Dullahan appear and engage the battle).

Dullahan is essentially a slight modification of his appearance in The Lost Age, so most of the strategy posted in the above section applies to this battle in the same way. Despite this version of Dullahan having a very slightly lower Attack statistic, he may be even harder than before because he has significantly-increased Defense and Agility statistics, as well as one all-new ability in his repertoire: the exact summon-stealing mechanic that Valukar used in his own boss battle in The Lost Age, "Crucible". So now, not only can he entirely defeat a summon-rush approach with a random Djinn Storm, he has a secondary chance to turn a summon-rush approach back at the party by using the highest-available summon sequence the party's Standby Djinn can allow for at the party itself, at the expense of the party's own Djinn. The higher agility also makes it harder for all party members to be able to unleash their summons before they are hit and potentially downed by Dullahan's abilities, and makes a Lull-based summon rush much harder to execute successfully. Despite all this, a similar summon-rushing tactic to The Lost Age is still the "standard" method of winning the Dullahan battle, though the chance it will fail will be higher. (Be sure never to allow Dullahan the Standby Djinn necessary for him to summon Coatlicue, since its extremely powerful regenerative effect will undo all of the damage you have accumulated on Dullahan.)

As for a traditional battling approach with a very highly-level party in high-tier classes, a variety of things makes this harder to pull off as well. In addition to the higher agility, Dullahan has higher Defense, which will partially mitigate some of the damage dealt by the party's physical attacks. Furthermore, the more randomized weapon unleash system of Dark Dawn will make attacking with weapons with a high unleash rate somewhat less effective on average, increasing the value of using Ronins with access to the Quick Strike Psynergy - but the "Four Ronin" approach mentioned in the previous section is partially defeated by the fact that only three Adepts can be Ronins (Himi does not have access to it), so some kind of substitute will have to be made to form a party that can possibly survive Dullahan's attacks after being hit by a Djinn Storm. Sveta in her Beastform is an extremely powerful but temporary option.

Nonetheless, battling Dullahan with a high-class party that does not require summons is a more appealing option in Dark Dawn than in The Lost Age, primarily because it is very easy to gain many levels in the endgame by repeatedly battling the Tua Warriors at Apollo Sanctum. Furthermore, every single battle with a Tua Warrior gives a guaranteed Water of Life, so all party members can be given a collection of the reviving items, which can help a party survive even a Djinn Storm if their levels are high enough.

Dullahan's statistics are as follows:

Dullahan, like in the previous game, regenerates 200 HP and 100 PP at the end of every turn, effectively granting him infinite PP.

Dullahan uses these battle commands:

Background and story
Dullahan has little provided context and even less relevance to the story in the Golden Sun games themselves. It is merely an extremely powerful entity resembling a large, animate suit of purplish-blue armor without a head, redesigned in its Dark Dawn appearance with a ghostly flame emitting from its head and a shield with a self-animating face (which may possibly represent Dullahan's "head"). It guards the capacity to summon Iris, "the sun's power", in both games it appears in - in The Lost Age, it is situated in the furthest depths of the Anemos Inner Sanctum near Contigo and the giant crater that was the former site of the City of the Anemos; originally, this allowed for speculation on its origins in regards to the Anemos culture, but Dark Dawn, taking place 30 years later, seemingly contradicts Dullahan's previous details by having him guard the Iris summon in a completely different location on practically the opposite end of Weyard, the Dark Dawn incarnation of Crossbone Isle (which also does not seem to adhere to much of the canon from its GBA appearance; as it is postgame-only content in a game with a story that resets to just before the final boss after the game is completed and saved as a postgame file, the Dark Dawn versions of Dullahan and Crossbone Isle may be intentionally non-canonical, spiritual carry-overs from the past games included strictly for gameplay's sake). Regardless of the game, when Dullahan is approached by the party of Adepts near the end of the game, he telepathically recites the following line before attacking the party:


 * “I am the shadow, the keeper of light. If you want the sun’s power, show me your own.”

In the meantime, the Necromage class in The Lost Age, provided by the Tomegathericon item, includes a Psynergy that resembles the user summoning an image of Dullahan to attack an enemy with its extremely powerful Fulminous Edge, in the same vein as earlier-level Psynergy that lets the user call on images of zombies and demons to attack the target. This is possible regardless of whether the real Dullahan in the Anemos Inner Sanctum has been defeated or not. It is unknown what relevance this has to the series lore.

Cultural references
The dullahan is a powerful fairy from Irish folklore, and is essentially the Irish version of the Grim Reaper (its name means "dark man"). It takes the form of a horseman who carries his head under his shoulder. This head has tiny, constantly flitting black eyes, a hideous ear to ear grin, and flesh the color and texture of moldy cheese. Often, the horse itself is headless, and the dullahan may drive a coach pulled by several such headless horses. Gates cannot stop the dullahan's journey--they just unbar automatically as it approaches. Once the dullahan stops riding, it calls out a name. The mortal who is named dies, and the dullahan drags his or her soul to the afterlife. Those who try to spy on the dullahan riding across the country are rewarded with a bucketful of blood splashed in their faces. Curiously, dullahans are terrified of gold--even a gold pin can drive them away from their task.

That dullahans are so closely associated with death is probably the reason why Necromages can call upon one to fight on their behalf, and why the boss can call on Charon so readily.

Trivia

 * As of Dark Dawn, Dullahan is the only summon-guarding "superboss" whose elemental weakness has no relation to the primary element of the summon it guards. In this case, Dullahan is vulnerable to Jupiter attacks but protects a Mars summon. By comparison, the other three superbosses in The Lost Age are weak to the element opposite of the summon they guard, while the two new guys in Dark Dawn are weak to the same element as their summon.
 * Dullahan is the enemy with the second-highest HP rating in Dark Dawn, behind the 16,066 HP of the fifth Ogre Titan.