Warning Spoiler Alert: This article or section contains details about plotlines not covered in the anime. Do not proceed unless you wish to be spoiled.
A Boss, in video game terminology, is a unique computer-controlled monster or character that is much more powerful than an average monster or non-player character encountered in the game until that point and usually serves as a challenge to the player at the end of particular section of a game, usually a level or stage, or guarding a specific objective.

In the Sword Art Online UniverseEdit

Throughout the Sword Art Online series, there are several types of bosses that can be encountered: Floor Bosses, Field Bosses, Flag Mobs and Dungeon Bosses. Most, but not all, bosses within the series, especially Floor Bosses, have "the" in their name to signify their uniqueness as bosses.

Floor BossEdit

A Floor Boss (フロアボス, Furoa Bosu?), alternatively called a Labyrinth boss, is a type of boss that can only be encountered in a large room, called a boss room, on the 20th floor of a Labyrinth in the castle of Aincrad. A Floor Boss's main purpose is to guard the entrance to the next floor, requiring players to defeat it to advance towards the 100th Floor. Each Floor Boss is a powerful creature, with several Hit Point (HP) bars, and usually has special attack patterns that are activated once the monster’s HP falls below a certain level. Some Floor Bosses also have minions that are constantly summoned throughout the battle to aid it in dealing with the players, though some bosses do not have minions at all.

74th Floor Boss Room

The 74th Floor's Boss Room that doubles as an Anti-Crystal Area.

The difficulty of each Floor Boss varies from floor to floor, with some causing little to no trouble, like the boss of the 22nd Floor, while others are extremely dangerous. The bosses on Aincrad's quarter floors are especially powerful and have led to numerous deaths in Sword Art Online. Normally, players may retreat from boss rooms by either using Teleport Crystals or retreating via the door if they can reach it in one piece, as bosses never leave the rooms they reside in, however, the boss rooms of the 74th and 75th Floors are designated as Anti-Crystal Areas, and it can be presumed that the remaining floors also host such effect, while the boss rooms starting with the 75th Floor automatically seal the players in a few minutes after they enter the room, completely preventing the chance of retreat during the battle.

Floor Bosses are also present in New Aincrad in New ALfheim Online. However, all of the Floor Bosses of the original Aincrad were replaced with brand new bosses[1] that, due to ALfheim Online not being a death game, are usually much more powerful than their counterparts in the original Aincrad. Like in the original Aincrad, there are exceedingly strong monsters every set number of floors; however, in New Aincrad, such a boss appears on every tenth floor instead of every twenty fifth.[2] Floor Bosses within New Aincrad also have their HP bars hidden from the players to make the battles even more difficult by making it harder to judge how much HP the boss has remaining. All boss rooms automatically seal the players in within a minute after they enter the room, with players even having the option to seal the boss rooms earlier by pressing a stone button on the wall next to the door.

Additionally, a new feature called the Monument of Swordsmen replaced the Monument of Life in New Aincrad. This new monument records the names of the players that participate in defeating a Floor Boss. However, as the monument is a 3D object within the world and hold a limited number of names in total, while it has to suffice for 100 floors, thus only the names of the party leaders that partake in the raid against the Floor Boss are added to the monument. Though, if a party of seven members or less manages to defeat the boss without any reinforcements, all the names of the members in that party are recorded on the monument.

Most Floor Bosses are best dealt with when the raiding party has as many players participating as possible, though there is an upper limit of up to forty-eight players in a single raiding party in Sword Art Online[† 1] and up to forty-nine players in New Aincrad in ALfheim Online[† 2].[3]

Known Floor BossesEdit

Image Name Floor
Original Aincrad Bosses
Illfang Illfang the Kobold Lord 1
Baran the General Taurus Baran the General Taurus 2 (CBT)
Progressive Vol 1 - 455 Asterius the Taurus King 2
Nerius the Evil Treant 3
Wythege the Hippocampus 4
Fuscus the Vacant Colossus Fuscus the Vacant Colossus 5
Two-headed giant 25
Metallic elemental 27
Six-armed metallic Buddha statue 50
Armoured stone warrior 60
The Gleam Eyes The Gleam Eyes 74
Skull Reaper's full appearance The Skull Reaper 75
Heathcliff Heathcliff 100
New Aincrad Bosses
Wadjet the Flaming Serpent 8
The Four-Armed Giant (anime) The Four-Armed Giant 27
Sleeping Knights and Kirito's group defeating 28th floor boss Large crustacean 28

Field BossEdit

A Field Boss (フィールドボス, Fīrudo Bosu?) is a named monster strategically placed at the entrance to a Labyrinth on most floors in Aincrad. The main function of this Boss is to prevent access to the Labyrinth of the floor until the monster is defeated. A Field Boss's den is usually surrounded by cliffs or ranging streams on both sides, arranged in such a way that there would be no way to access the Labyrinth until the Boss is defeated. Like Floor Bosses, each Field Boss can only be defeated once, however, they are much easier to defeat and can be defeated by a single party, if all members are sufficiently leveled and have enough experience in battle.

Not all floors have a field boss. For example the 1st Floor and the 22nd Floor did not have any.

Known Field BossesEdit

Image Name Floor
Bullbous Bow Bullbous Bow 2
Biceps Archelon Biceps Archelon 4
Geocrawler1 Geocrawler 56

Flag MobEdit

A Flag Mob (フラグ Mob, Furagu Mob?) is a monster set up for the completion of a quest or event. These type of monsters can spawn between every few hours to every few days, while some Flag Mobs only spawn once a year or do not re-spawn at all. Some rare Flag Mobs that are as powerful as a Boss monster usually also drop rare and valuable items upon being killed, while other Flag Monsters are barely more difficult than a regular monster. Some Flag Mobs are part of quests that have sub-routes, thus a certain event may be triggered during the quest that would help defeat the boss, for example, taking a certain sub-route may lead to a temporary NPC partner for the quest.

Known Flag MobsEdit

Image Name Location Comment
Sword Art Online
Nephila Regina Nephila Regina In the Queen Spider Nest on the 3rd Floor. A dungeon boss that needs to be killed for the «Vanquishing the Spiders» quest.
Fallen Elf Commander 3rd Floor The boss that needs to be defeated for the «Retrieving the Key» quest.
The King of Lakes The King of Lakes Lake on the 22nd Floor A fishing event boss that drops a rare fishing rod.
The Witch of the West Quest area on the 22nd Floor A boss that is required to be killed for the «Witch of the West and the Three Treasures» quest.
Sword Art Online 03 Nicholas The Renegade Forest of Wandering Christmas event boss that drops a revival item called Divine Stone of Returning Soul.
ALfheim Online
Kraken the Abyss Lord Kraken the Abyss Lord Undersea Temple The NPC that gives players the «Deep Sea Plunderers» quest to steal the Prince's Egg from the Undersea Temple and becomes a boss if the players refuse to turn in the egg.
Thrym Thrym Thrymheim The boss required to be killed for the completion of «The Holy Sword of the Ice Palace» quest.

Dungeon BossesEdit

A Dungeon Boss is a stronger than average and, usually, named monster that appears in dungeons (field dungeon/sub-dungeon) to either impede player progress towards clearing the dungeon, for example, by guarding the stairs to the next floor of the dungeon, or for guarding the treasure at the end of the dungeon. Some Dungeon Bosses also double as Flag Mobs for certain quests, like in Thrym's case, while some were meant to ensure that players could never access special areas of a dungeon.

Known Dungeon BossesEdit

Image Name Location
Sword Art Online
Nephila Regina Nephila Regina In the Queen Spider's Nest on the 3rd Floor
White dragon X'rphan the White Wyrm West Mountain
The Fatal Scythe The Fatal Scythe Hidden Dungeon
ALfheim Online
Cyclops Thrymheim's 1st floor[4]
Black Minotaurus Black Minotaurus Thrymheim's 2nd floor.
Golden Minotaurus Golden Minotaurus Thrymheim's 2nd floor.
Thrymheim 3rd floor boss Centipede-like giant Thrymheim's 3rd floor
Thrym Thrym Thrymheim final floor


  1. Up to eight parties with a maximum of six players each
  2. Up to seven parties with a maximum of seven players each


Start a Discussion Discussions about Boss

  • New Aincrad Floor 21 Boss

    • The wiki forgot to mention the stone golem that was the Floor 21 Boss of New Aincrad. I am assuming it was the Floor Boss and not a field bo...
  • Source

    3 messages
    • 27th probably comes from The Day After. 60th comes from Morning Dew Girl, according to the reference on Aincrad's article.
    • Thanks.

Ad blocker interference detected!

Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.