Boss

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. Most, but not all, bosses within the series, especially Floor Bosses, have "the" in their name to signify their uniqueness as bosses.

Floor Boss
A Floor Boss (フロアボス), 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.

Initially, the dungeon's Boss will not be present within the Boss Room or will passively await combat. Only once a player has stepped far enough inside or a player reaches the back of the Boss Room and destroys a key object will the Boss become hostile. Once in combat, the Boss's HP bars are displayed above the Monster's body. 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. Upon leaving, the boss will lose all aggro and all HP damage previously dealt will heal very quickly. Sometimes the entrance doors will lock behind players due to the boss's abilities or theme yet the door can still be opened from the outside by other players. Example factors that lock the door include the flooding of the room, part of the Boss blocking the entrance way , or the door remaining sealed until a puzzle is solved. 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.

Upon defeat, the Teleport Gate on the next Aincrad Floor will automatically open after two hours, allowing public access from all the previously opened lower Aincrad Floors. Alternatively, if a player reaches the main city of the next Aincrad Floor and touches the Teleport Gate within the two hour window, this will open the Teleport Gate early. For thirty minutes or so after defeating the Floor Boss, the spawn rate of monsters is drastically decreased on the followed Aincrad Floor above. This effect is only active in the area around the main town of the Floor.

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 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. 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 and up to forty-nine players in New Aincrad in ALfheim Online.

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

Field Boss
A Field Boss (フィールドボス) 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.

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

Flag Mob
A Flag Mob (フラグ 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.

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, like in Thrym's case, while some were meant to ensure that players could never access special areas of a dungeon. In Sword Art Online, unlike other single-elimination Bosses, regular Dungeon Bosses respawn after some time.