The Fatal Scythe

«The Fatal Scythe» (ザ・フェイタルサイズ) is the Boss of the hidden dungeon located beneath the Town of Beginnings on the first floor. Its armaments include a large powerful scythe, and a long, ragged black cloak. It was fought by Asuna and Kirito when they were trying to help Yulier rescue her guild leader, Thinker, who had been trapped in the area's safe zone. Its battle level is unknown, but Kirito suspected it to be as powerful as the 90th Floors' bosses. This was proven when it was able to send both Kirito and Asuna flying, despite them blocking its strike together. It was only through the intervention of Yui that The Fatal Scythe was defeated.

It is unclear, but one can easily assume that Kirito and Asuna would not have survived the fight, had Yui not intervened by using the GM console.

Appearance
The Fatal Scythe greatly resembles the Grim Reaper, being skeletal in appearance, being massive in size as with other bosses, and being clad in a tattered black robe (red inside) and carrying a large silver scythe.

Abilities
The Fatal Scythe is an extremely powerful boss, befitting its name, one swing from its scythe could send both Kirito and Asuna flying, as well as depleting about half of their HP with just one strike. Its main weapon is a scythe as large as itself. It is known that The Fatal Scythe was not present in SAO's closed beta test, as Kirito could not identify it, though he speculated it to be as powerful as a boss from the 90th Floor, which considering its immense strength, does not seem too far fetched.