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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 a particular section of a game, usually a level or stage, or guarding a specific objective.

In the Sword Art Online Universe

Throughout the Sword Art Online series, there are several types of bosses that can be encountered: Floor Bosses, Mid-Bosses, Field Bosses, Flag Mobs and Dungeon Bosses.

In Sword Art Online, the two major groups of bosses are Field Bosses and Floor Bosses. It is common knowledge that superior bosses are distinguished from weaker bosses by a definite article ("the") in their names. Such monsters are colloquially referred to as Bosses-with-THE (ザつきボス, Za Tsuki Bosu?) by the players. However, unbeknownst to the majority of the player base, there are actually two types of bosses that fall under this category: ones that have a proper name before the definite article and title, and ones that do not have any proper name before the article. Contrary to expectations, bosses that do not have any proper name are actually considered more dangerous than ones that do have a proper name. According to the game's lore, these bosses were so feared by the populace that nobody even dared speak their names, which led to the names being forgotten entirely over the course of many years.[1]

Floor Boss

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 boss room, a large room located on the highest 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 that are displayed over its body; special attack patterns are usually triggered once the monster's hit points fall below a certain level.[citation needed] However, the actual difficulty of each Floor Boss varies from floor to floor: some cause little to no trouble, such as the boss of the 22nd Floor,[citation needed] 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.[2] The second-most-powerful bosses are located on floors that are multiples of ten.[3] 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.

Initially, a Floor Boss will either not be present within the Boss Room at all, or will at least passively await combat. The boss will only appear in the room or leave its passive state once a player has stepped far enough inside the room.[4]

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

Normally, players may retreat from boss rooms by either using Teleport Crystals or leaving the room via the door if they can reach it safely, as bosses never leave the rooms they reside in.[5] Upon all players leaving the room, which results in the boss disengaging from its aggressive state, all damage previously dealt to the boss will heal very quickly.[6] Sometimes the entrance doors will lock behind players due to the boss's abilities or theme; however, the door can still be opened either by other players from the outside, or through gimmicks inside the room. Example factors that lock the door include: flooding of the room until a player opens the door from the outside[7], part of the boss blocking the entrance[6], or the door remaining sealed until a puzzle is solved.[8] The boss rooms of the 74th and 75th Floors are designated as Anti-Crystal Areas, while the boss room of the 75th Floor also automatically sealed the players inside the room a few minutes after they entered the room, completely preventing the chance of retreat during the battle.

Following a Floor Boss's defeat, the Teleport Gate on the next Aincrad Floor will automatically open after a period of two hours, allowing public access to the new Floor from all the previously-opened lower Aincrad Floors.[9] Alternatively, the gate may be opened early if a player reaches the main settlement of the next Aincrad Floor and touches the Teleport Gate within the two hour window.[9] For thirty minutes or so after the players defeat a Floor Boss, the spawn rate of monsters is drastically decreased on the following Aincrad Floor. This effect is only active in the area around the main settlement of the Floor.[10]

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[11] 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.[12] 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].[13] It is possible for more players to join a boss battle and there have actually been instances where players formed two raid parties for a single boss, such as during the battle against the boss of the 25th Floor; however, it becomes harder to coordinate the players when more than one raid party is present during a battle.[14]

Known Floor Bosses

Image Name Japanese Floor Outcomes Ref
Original Aincrad Bosses
Illfang.png Illfang the Kobold Lord イルファング・ザ・コボルド・ロード
(Irufangu za Koborudo Rōdo)
1 Defeated on December 4, 2022

Casualties: Diavel
Drops: Coat of Midnight

Progressive Vol 1 - 455.png Asterius the Taurus King アステリオス・ザ・トーラスキング
(Asuteriosu za Tōrasu Kingu)
2 Defeated on December 14, 2022
Nerius the Evil Treant.png Nerius the Evil Treant ネリウス・ジ・イビルトレント
(Neriusu ji Ibiru Torento)
3 Defeated on December 21, 2022
Wythege the Hippocampus ウィスゲー・ザ・ヒッポカンプ
(Wisugē za Hippokampu)
4 Defeated on December 27, 2022
Fuscus the Vacant Colossus.png Fuscus the Vacant Colossus フスクス・ザ・ヴェイカントコロッサス
(Fusukusu za Veikanto Korossasu)
5 Defeated on December 31, 2022
The Irrational Cube.png The Irrational Cube ジ・イレーショナル・キューブ
(Ji Irēshonaru Kyūbu)
6 Defeated on January 4, 2023 [15]
Aghyellr the Igneous Wyrm アギエラ・ジ・イグニアス・ウィルム
(Agiera Ji Iguniasu Virumu)
7 [16]
Kagachi the Samurai Lord.png Kagachi the Samurai Lord カガチ・ザ・サムライロード
(Kagachi za Samurai Rōdo)
10 [17]
The Storm Griffin.png The Storm Griffin ザ・ストームグリフィン
(Za Sutōmu Gurifin)
11 [17]
The Strict Hermit.png The Strict Hermit ザ・ストリクトハーミット
(Za Sutorikuto Hāmitto)
12 [17]
The Dire Tusk.png The Dire Tusk ザ・ダイアータスク
(Za Daiā Tasuku)
18 [17]
Unnamed two-headed giant N/A 25
Unnamed metallic elemental N/A 27
Waheela the Black Wolf.png Waheela the Black Wolf ワヒーラ・ザ・ブラックウルフ
(Wahīra za Burakku Urufu)
28 [17]
Bracken the Prison Warden ブラッケン・ザ・プリズンワーデン
(Burakken za Purizun Wāden)
40 Defeated on October 18, 2023 [14]
Unnamed six-armed metallic Buddha statue N/A 50 Drops: Elucidator[18]
Unnamed armoured stone warrior N/A 60
The Gleam Eyes.png The Gleam Eyes ザ・グリーム・アイズ
(Za Gurīmu Aizu)
74 Defeated on October 18, 2024

Casualties: Kobatz, 2 other ALF members.

Skull Reaper's full appearance.png The Skull Reaper ザ・スカル・リーパー
(Za Sukaru Rīpā)
75 Defeated on November 7, 2024

Casualties: 10 (scouts)[2] + 14 (boss battle)

Dorz'l the Chaos Drake.png Dorz'l the Chaos Drake ドルゼル・ザ・カオスドレイク
(Doruzeru za Kaosu Doreiku)
91 N/A [17]
Heathcliff.png Heathcliff 100 N/A
Superseded Aincrad Bosses
Baran the General Taurus.png Baran the General Taurus バラン・ザ・ジェネラルトーラス
(Baran za Jeneraru Tōrasu)
2 N/A
N/A The Irritating Cube ジ・イリテーティング・キューブ
(Ji Iritētingu Kyūbu)
6 N/A
An Incarnation of the Radius.png An Incarnation of the Radius アン・インカーネイト・オブ・ザ・ラディウス
(An Inkāneishon Obu za Radiusu)
100 N/A
New Aincrad Bosses
Wadjet the Flaming Serpent.png Wadjet the Flaming Serpent ワジェト・ザ・フレイミング・サーペント
(Wajeto za Fureimingu Sāpento)
The Four-Armed Giant (anime).png Unnamed four-armed giant N/A 27 Defeated on January 8, 2026
Sleeping Knights and Kirito's group defeating 28th floor boss.png Unnamed large crustacean N/A 28


In Sword Art Online, a Mid-Boss (中ボス, Chū Bosu?) is a boss-class monster that impedes travel between the floors of a Labyrinth Tower[3] or a boss-class monster that supports the Floor Boss.[21] Unlike regular Floor Boss minions, Mid-Bosses grant a Last Attack Bonus on defeat.[21]

Known Mid-Bosses

Image Name Japanese Location Outcomes Ref
Nato the Colonel Taurus.png Nato the Colonel Taurus ナト・ザ・カーネルトーラス
(Nato za Kāneru Tōrasu)
In the 2nd Floor boss room. Defeated on December 14, 2022
Baran the General Taurus.png Baran the General Taurus バラン・ザ・ジェネラルトーラス
(Baran za Jeneraru Tōrasu)
In the 2nd Floor boss room. Defeated on December 14, 2022

Drops: Gold bull-pattern boxers

N/A Unnamed ophidian-type boss N/A 5th floor of the Labyrinth. Defeated on January 4, 2023 [22]
Ruthless Warder Chief.png Ruthless Warder Chief ルースレス・ワーダーチーフ
(Rūsuresu Wādā Chīfu)
The stairway between the 23rd and 24th floors of the Labyrinth on the 40th Floor of Aincrad. Defeated on October 15, 2023 [3]

Field Boss

A Field Boss (フィールドボス, Fīrudo Bosu?) is a named monster strategically placed somewhere between the Teleport Gate and the entrance to each Labyrinth. The main function of these bosses are to prevent access to the Labyrinth of the floor until the monsters are 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.[23][22]

Not all floors contain a Field Boss. An example of this exception is the 22nd Floor, which did not have Field Bosses. On the other hand, certain Floors may contain multiple Field Bosses, such as was the case with the 6th Floor of Aincrad.[citation needed] Unlike Floor Bosses, Field Bosses can be beaten an unlimited number of times, as they respawn over time.[24]

Known Field Bosses

Image Name Japanese Floor Outcomes Ref
Unnamed giant boar-type Field Boss N/A 1 [25]
Bullbous Bow.png Bullbous Bow ブルバス・バウ
(Burubasu Bau)
2 Defeated on December 9, 2022

Drops: Chakram[† 3]

The Indolent Treent ジ・インドレント・トレント
(Ji Indorento Torento)
3 [24]
Biceps Archelon.png Biceps Archelon バイセプス・アーケロン
(Baisepusu Ākeron)
4 Defeated on December 24, 2022
N/A Unnamed vine plant-type Field Boss N/A 6 Defeated on January 2, 2024

Drops: A large amount of peas.

N/A Basalt Morpha バサルトモルファ
(Basaruto Morufa)
6 Defeated on January 4, 2024 [22]
N/A Unnamed carnivorous plant-type Field Boss N/A 6 Defeated on January 4, 2024 [22]
Zehghi the Flame Caller.png Zehghi the Flame Caller ゼーギ・ザ・フレイムコーラー
(Zēgi za Fureimu Kōrā)
11 [17]
White dragon.png X'rphan the White Wyrm 白竜ゼーファン(ゼーファン・ザ・ホワイトウィルム)
(Zēfan za Howaito Wirumu)
55 [1]
Geocrawler1.png Geocrawler ジオクロウラー
56 Defeated on March 7, 2024

Flag Mob

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 Mobs

Image Name Japanese Location Notes Drops Ref
Sword Art Online
Nephila Regina.png Nephila Regina ネフィラレジーナ
(Nefira Rejīna)
In the Queen Spider Nest on the 3rd Floor. A dungeon boss that needs to be killed for the «Vanquishing the Spiders» quest.
Fallen Elven Commander.png Fallen Elf Commander フォールン・エルフ・コマンダー
(Fōrun Erufu Komandā)
3rd Floor The boss that needs to be defeated for the «Retrieving the Key» quest.
The King of Lakes.png The King of Lakes 湖のヌシ
(Mizūmi no Nushi)
Lake on the 22nd Floor A fishing event boss that drops a rare fishing rod. Rare fishing rod
The Witch of the West 西の魔女
(Nishi no Majo)
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.png Nicholas The Renegade 背教者ニコラス
(Haikyousha Nikorasu)
Forest of Wandering Christmas event boss that drops a revival item called Divine Stone of Returning Soul. Divine Stone of Returning Soul
ALfheim Online
Kraken the Abyss Lord.png Kraken the Abyss Lord クラーケン・ジ・アビスロード
(Kurāken ji Abisu Rōdo)
Undersea Temple The NPC that gives players the «Deep Sea Plunderers» quest to steal the The Child's Egg from the Undersea Temple and becomes a boss if the players refuse to turn in the egg.
Thrym.png Thrym スリュム
Thrymheim The boss required to be killed for the completion of «The Holy Sword of the Ice Palace» quest.

Dungeon Bosses

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, such as in the case with Thrym, while some were meant to ensure that players could never access special areas of a dungeon.[citation needed] In Sword Art Online, regular Dungeon Bosses respawn after some time, unlike Floor Bosses and Field Bosses.[27]

Known Dungeon Bosses

Image Name Japanese Location Outcomes Ref
Sword Art Online
Nephila Regina.png Nephila Regina ネフィラレジーナ
(Nefira Rejīna)
In the Queen Spider's Nest on the 3rd Floor
Feral Warder Chief.png Feral Warder Chief フィーラル・ワーダーチーフ
(Fīraru Wādā Chīfu)
A dungeon on the 40th Floor. Casualties: Yuna [14]
The Fatal Scythe.png The Fatal Scythe ザ・フェイタルサイズ
(Za Feitaru Saizu)
Hidden Dungeon
ALfheim Online
Unnamed cyclops N/A Thrymheim's 1st floor [28]
Black Minotaurus.png Black Minotaurus ? Thrymheim's 2nd floor.
Golden Minotaurus.png Golden Minotaurus ? Thrymheim's 2nd floor.
Thrymheim 3rd floor boss.png Unnamed centipede-like giant N/A Thrymheim's 3rd floor
Thrym.png Thrym スリュム
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
  3. Only in the manga.