The Fatal Scythe

«The Fatal Scythe» is the boss of the hidden dungeon located beneath the Starting City on the first floor. Its armaments include a large powerful scythe, ability to phase in and out of walls at a tremendous speed. It was fought by Asuna and Kirito when they were trying to help Yulier find her guild's 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, proven when it was able to deplete a large number of both Kirito's and Asuna's health with merely one swing of its scythe. 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 robe and carrying a large 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 despite them blocking together, as well as depleting a large amount of their HP with only one strike. Its main weapon is a scythe as large as it itself is, with which, it was able to blow away the likes of Kirito and Asuna. 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 power, doesn't seem too farfetched.