Me and Mothrayas have done "How good is ___?" videos, and I decided to compile a list of how good each weapon is. The first number is bosses killed, and the second number is damage on the next boss using the remaining ammo. All numbers are assuming you're attacking the boss that would take the most damage.
Shadow Blade
Needle Cannon
Ring Boomerang
Mega Man 2
(5)
Metal
Quick
(3 + 16 Damage)
Heat (Normal)
(3 + 4 Damage)
Air (Normal)
(3)
Bubble
(2 + 6 Damage)
Air (Difficult)
(2)
Heat (Difficult)
(1 + 18 Damage)
Crash (Normal)
(1 + 16 Damage)
Heat (Difficult)
(1)
Wood
Crash (Difficult)
(14 Damage)
Flash
Mega Man 3
(7)
Top Spin*
Glitched Needle**
Glitched Shadow**
(6 + 14 Damage)
Needle
(5 + 10 Damage)
Shadow
(2 + 17 Damage)
Spark
(2 + 15 Damage)
Snake
(2 + 6 Damage)
Hard
Gemini
(2)
Magnet
*Apparently, you can use Top Spin and not use any ammo. If this was done, all but Hard Man could be killed, but avoiding death is also an issue.
**By Pausing and switching weapons in between ammo uses, the shots per ammo point gets reset to 0. Hard Man is immune to both.
Mega Man 4
(8)
Glitched Ring*
(7)
Glitch Pharaoh**
(3 + 9 Damage)
Pharaoh***
(2 + 22 Damage)
Dust
(1 + 21 Damage)
Ring
Drill
(1 + 18 Damage)
Dive
(1 + 14 Damage)
Skull
(1 + 13 Damage****)
Bright
(1)
Toad
*Technically, you can manuever to keep Ring Boomerang going. This is theoertical and may be impossible to kill all 8.
**Using the Pause Glitch, you can avoid running out of ammo, but Pharaoh doesn't affect Skull Man.
***This is without pausing, and since you can charge without using ammo by taking damage, 28 shots are possible.
****Although Bright affects all bosses, it runs out. It takes 5 uses to kill a boss and the remaining 2 can do 13 damage.
Mega Man 5
(1 + 21 Damage)
Gyro
Napalm
Stone
Charge
(1 + 18 Damage)
Crystal
(1 + 7 Damage)
Star
Wave
(1)
Gravity
Mega Man 6
(2 + 7 Damage)
Flame
(1 + 21 Damage)
Yamato
Wind
Knight
Tomahawk
(1 + 3 Damage)
Blizzard
(1)
Plant
Centaur
Mega Man 2-6
(8)
Glitched Ring
(7)
Glitch Pharaoh
Top Spin
Glitched Needle
Glitched Shadow
(6 + 14 Damage)
Needle
(5 + 10 Damage)
Shadow
(5)
Metal
Quick
(3 + 16 Damage)
Heat (Normal)
(3 + 9 Damage)
Pharaoh
(3 + 4 Damage)
Air (Normal)
(3)
Bubble
(2 + 22 Damage)
Dust
(2 + 17 Damage)
Spark
(2 + 15 Damage)
Snake
(2 + 7 Damage)
Flame
(2 + 6 Damage)
Air (Difficult)
Hard
Gemini
(2)
Heat (Difficult)
(1 + 21 Damage)
Yamato
Wind
Knight
Tomahawk
Gyro
Napalm
Stone
Charge
Ring
Drill
(1 + 18 Damage)
Dive
Crash (Normal)
Crystal
(1 + 16 Damage)
Heat (Difficult)
(1 + 14 Damage)
Skull
(1 + 13 Damage)
Bright
(1 + 7 Damage)
Star
Wave
(1 + 3 Damage)
Blizzard
(1)
Plant
Centaur
Wood
Crash (Difficult)
Gravity
Toad
(14 Damage)
Flash
