The Skull Reaper was a very large boss that resembled a skeletal centipede with an elongated skull for a head and red shining eyes. The majority of the creature's bones, including its arms, legs, and rib cage functioned like scythes.
Prior to Kirito and Asuna's return to the Knights of the Blood, a twenty-member scouting party from five different guilds was preparing for the boss fight. When the first ten reached the center of the room, the entrance closed. The gate reopened five minutes later and neither the ten players nor the boss were seen. Like the previous boss, the battle area was also in an anti-crystal area, preventing the ten players from exiting the boss room.
The Skull Reaper is the most lethal of the Labyrinth bosses seen so far, easily claiming the lives of 14 players before being slain in battle. Despite being weaker than The Fatal Scythe, The Skull Reaper still inflicts large amounts of damage even with short combo attacks, being able to kill high-level players with just one hit, and even forcing Asuna to assist Kirito in blocking its scythe arm.
The Skull Reaper, befitting its centipede-like appearance, was able to move very quickly to outmaneuver the players, making it extremely difficult to avoid being hit by its attacks. Its huge and long body also makes it difficult to avoid the creature's strikes. The Skull Reaper also has an irregular targeting pattern (like most of the monsters on Floor 70+), as it ignored Heathcliff's shield after he blocked the attack in favor of killing the player he protected from its previous attack.
- 10 players were killed during the recon of the Skull Reaper.
- 14 players died during the second attempt of clearing the 75th Floor.
- The Skull Reaper is one of the four quarter (every 25 Floors) bosses in Aincrad. Like other such bosses, The Skull Reaper is much more powerful and dangerous than the bosses of adjacent Floors.
- The Skull Reaper is the first known boss in the Aincrad Arc with a known number of HP bars that has five health bars instead of four, suggesting that the bosses above it have a similar amount or higher.
- The arena of this boss surpasses the size of any other boss arena in the Aincrad Arc, as there is one large platform and multiple smaller platforms around the large platform.