Superbosses

Similar to other MMOs or the rest of the series, Dragon Quest X has a handful amount of Superbosses added through some of the later versions, unlike the average bosses available through the main story, these require strategy and make the most use of all the vocations available. To make the entry point more easy for new players getting into these bosses, most of these have different levels of difficulty between I through V.

Version 3: Everdark War (常闇の聖戦)
The Everdark War consist on endgame content where you fight against powerful bosses inhabiting the continent of Nadragand. During v3.1 throught the rest of version 3, three bosses were added on three different realms. The strength of each one used to depend on what the current time (JST) was but, since v5.0 they included a fifth difficulty (Strength V) and the ability to select the Strength by yourself. Hand 5 Dragonite fangs (you used to need 10 before v5.5), interact with the corresponding NPC/Teleportal and you have 20 minutes to finish the battle.

Unlock Requirements

 * Clear v3.1 Story (v3.3 and v3.5 for the subsequent bosses)

About Dragonite fangs
As mentioned before, you need a material item called "Dragonite", these fangs are 100% required to start the battle. The fang collection starts by talking to the Guide NPC (Prinella, Management terminal Q485, Dark), they have an option to cast a "charm spell" on you, this spell grants you a 100% chance to get "Dragonite Shards" as drop from a monster selected by the NPC (there's also a 10% chance to get a "Dragonite" fang).

This monster won't change until the next day at 6:00 JST and it can be one of the following: You can also buy Dragonite fangs through Bazaar if you don't want to spend time grinding. After collecting enough shards, go to the corresponding NPC, you can exchange 10 "Dragonite Shards" for 1 "Dragonite" fang.
 * Axesaurus (アックスドラゴン)
 * Dragster (ヘルジュラシック)
 * Elder Dragon (エルダードラゴン)
 * Mandrake Militant (アッシュリザード)
 * Drakulurch (ベヒードス)

If you manage to defeat the boss, the 5 Dragonite fangs you used will disappear from your Item bag, otherwise they won't.

The Superbosses

 * Everdark Dragon Regnad (常闇の竜レグナード)
 * Located in the Fire Realm, Valley of Fire's Matil Village
 * Talk to Prinella, prepare your 5 Dragonite fangs, select the difficulty and start the fight.
 * Dark King (ダークキング)
 * Regnad must be defeated once at any level before Dark King is available.
 * Clear v3.3 Story and go to Dark Realm's Utopia
 * Speak to Management terminal Q485 and write in Nearby's Chat (the white one): 「りゅうとうしがあらわれた！コマンド？」
 * After that a Teleportal will appear, speak to it, select the difficulty and start to fight.
 * Sea Lord Meiv (海冥主メイヴ)
 * Dark King must be defeated once at any level before Meiv is available.
 * Clear v3.5 Story and go to Storm Realm, Town of Must's Abandoned Church
 * Prepare your 5 Dragonite fangs and talk to Dark, select the difficulty and start the fight.

Rewards
A purple (only appears once a day) and a red treasure box will appear, containing the following rewards:

Based on the Strength (I, II, III, IV, V, drop amount goes by:

Version 4-5: Battle of the Holy Guardians (聖守護者の闘戦記)

 * Demon Corpse Legirrazzo & Demon Beast Logast (冥骸魔レギルラッゾ＆獣魔ローガスト)
 * Red Demon Scorpide (紅殻魔スコルパイド)
 * Green General Gelzark (翠将鬼ジェルザーク)
 * Brutal Beast Gardodon (剛獣鬼ガルドドン)
 * Blue Armor Delmeze (邪蒼鎧デルメゼ)
 * Evil Spirit Barashna (羅刹王バラシュナ)

Version 6: Criminals of the Abyss (深淵の咎人たち)

 * Ruberangis the Vile (厭悪のルベランギス)