The Weapons Archive (ウェポンアーカイブ Wepon Ākaibu, "Weapon Archive") is the boss of the first Wily Castle stage from Mega Man 10. It is a room with Special Weapon data of Robot Masters from previous games, and contains three blocks that can fly and attack with the weapon of one Robot Master. There are three Weapons Archives in the stage, the first room containing data of Elec Man, Wood Man, and Gemini Man; the second data of Ring Man, Napalm Man, and Flame Man; and the third data of Slash Man, Frost Man, and Tornado Man. Each block has a weakness similar to that of the robot whose data is being copied. For example, Elec Man's block is weak against a cutter weapon, Gemini Man's block is weak against a weapon that travels along floors and walls, and Ring Man's block is weak against a fire weapon, just like their original counterparts.
Every Robot Master data pod has its own weakness to one of the Special Weapons in Mega Man 10.
- As with everything weak to Chill Spike (except for the Wily Capsule), Commando Bomb, and Thunder Wool, the weakness only counts for indirect hits.
- Judging by how Elec Man and Wood Man are included, most of the robot masters in the Weapons Archive are Keiji Inafune's favorite creations, or at least the ones he likes the most from each game. Tornado Man is also sometimes believed to be a favorite among the developers of Mega Man 9, furthering the concept that the nine chosen Robot Masters who appear are the developer favorites from each previous numbered game.
- There are 72 blocks in the background of these bosses (4 are obscured by the screen). Three of these blocks are lit up during combat. Counting from left to right, each lit block corresponds to the serial number of a currently loaded Robot Master.
- The usage of previous games' weapons in this game is very similar to Doc Robot in Mega Man 3, since Doc Robot used the powers of Mega Man 2's Robot Masters in that game. The "bridge" from Mega Man IV also used weapons from other bosses, but the bosses are from the same game.
- The Mega Man 7 and Mega Man 8 Robot Masters' graphics were changed to 8-bit style to fit the game, as Slash Man and Frost Man were originally drawn in 16-bit and 32-bit, respectively.
- Despite being shown as a main adventure in Mega Man 9, there wasn't any Robot Master data from Mega Man & Bass even though including either Tengu Man or Astro Man could easily have represented both games. This further hints at the theory that the nine chosen bosses are developer favorites, as a weapon that could substitute for Tengu Man's weakness (the Chill Spike) is avaliable to the player. Oddly, Frost Man was a fan submission while both of the aforementioned bosses were Capcom creations.
- As mentioned before, each block has a weakness similar to that of the robot whose data is being copied.
- Elec Man: The Wheel Cutter and Rolling Cutter are cutter-themed weapons.
- Wood Man: The Triple Blade and the Air Shooter are both weapons that spilt into three separate projectiles after being fired. In addition, the Triple Blade and the Metal Blade are both cutter-themed weapons. Even though Wood Man's other, more prominent weakness was Atomic Fire, a fire weapon, Solar Blaze does normal damage.
- Gemini Man: The Wheel Cutter and the Search Snake are both weapons which travel along walls and floors.
- Ring Man: The Solar Blaze and the Pharaoh Shot are both fire weapons. Furthermore, Pharaoh Man has an attack that sends out waves of fire much like the Solar Blaze does upon splitting and the Solar Blaze before splitting resembles the charged Pharaoh Shot.
- Napalm Man: The Rebound Striker and the Crystal Eye are both large blunt spheres that can bounce off walls.
- Flame Man: Due to the lack of a wind weapon, with Wind Storm being his weakness in Mega Man 6, the Water Shield was the most ideal choice.
- Slash Man: The Chill Spike and the Freeze Cracker are both ice weapons. Oddly, Slash Man's other weakness, the Scorch Wheel, was not similarly duplicated: the Solar Blaze does only normal damage. The fact that Slash Man's block only takes severe damage from the spiked form of the Chill Spike may be a reference to Mega Man & Bass's Burner Man, who can be pushed onto spikes with another ice-themed weakness, the Ice Wall.
- Frost Man: The Commando Bomb and Flash Bomb are both explosive weapons. Like with Slash Man, Frost Man's weakness to a fire-type weapon, the Flame Sword, was not replicated, even though Flame Sword deals more damage than the Flash Bomb per hit.
- Tornado Man: The Thunder Wool and the Plug Ball are both electric weapons.
- The amount of damage each weapon deals to the blocks is also based upon previous games. For example, Elec Man's block is destroyed with three hits of the Wheel Cutter - Elec Man can also be destroyed with three hits of the Rolling Cutter in the original Mega Man.
- Many of the weapons used by the Weapons Archive are slower and weaker than their original counterparts, the most notable example being Elec Man's Thunder Beam; in Mega Man, the Thunder Beam did 10 damage to Mega Man, but that is not the case here. The Gemini Laser used by Gemini Man's data, however, is faster than it originally was, though this may be because the laser caused moderate lag in Mega Man 3 when fired by either the boss or the player.
- Some additional moves of each boss are not replicated, mostly due to the fact that the room does not contain the proper environments: for instance, the eggs that Slash Man tosses from the ceiling in his Mega Man 7 boss fight are not used by the archive version, as there is no concealed portion of the ceiling in the archive room, and Frost Man's "panic" move, where he causes all the ice blocks in his boss chamber to fall, is not replicated either, for the obvious reason that there is no conveyor belt of ice blocks.