Too long didn't read: It does the same damage as cold iron vanquisher but it's a brandish.
Data regarding Amputator: (Tier 2, neutral target, max damage)
Damage per combo: 116 / 142
Damage per charge: 202 / 75
Damage per combo, no damage bonus, vs slime: 99 / 123
Damage per combo, no damage bonus, vs not slimes: 82 / 103
For comparison:
Data regarding Acheron: (Tier 2, neutral target, max damage)
Damage per combo: 160 / 209
Damage per charge: 317 / 80
Damage per combo (T2 damage VS undead, max damage): 98 / 125
Damage regarding Combuster/Obsidian Edge: (Tier 2, neutral target, max damage)
Damage per combo: 141 / 180
Damage per charge: 287 / 72
Damage from fire: 33, 3 ticks, 99 total (this will vary based on monster defense)
Data regarding Leviathan Blade/Celestial Saber: (Tier 2, neutral target, max damage)
Damage per combo: 129 / 157
Data regarding Cold Iron Vanquisher: (Same conditions)
Damage per combo: 116/142
Unless it suddenly does something magical when I finish heating it.... (T3 items in T2 aren't effected by heat, damage-wise)
I DUB THEE TRASHERON
EDIT-
SkepticRaven posted some damage numbers as well, from a heated+level 10 version-
http://forums.spiralknights.com/en/node/117917#comment-1049824
Euclidian-Space made a video of himself using the weapon-
http://forums.spiralknights.com/en/node/117917#comment-1049976
Upsides to Amputator:
It's a chainsaw blade. Enough said.