Circular Saw

From: Melee

Damage: 300 swing / 200 per cycle (aim + attack, held)
Slots: 1
Ammo: none

How to get it

Finish the game in under 4 hours on any difficulty (Easy is fine). It appears in the Item Box of every save; if you discard it, it goes back to the box.

Verdict

The best weapon in the game: do the under-4-hours run before Madhouse.

Hold ZL + ZR for the continuous cut; the cycle rate is tied to the frame rate.
Kills Morgue Jack in seconds, shreds Marguerite in the Greenhouse (aim for the thing on her belly) and Mutated Jack's eyes.
Against Jack in the car in the Garage it does +100%.
On Madhouse it is practically mandatory (though several guides prefer ranged weapons for Madhouse Mutated Jack).

The same condition unlocks the X-Ray Glasses.

Nightmare: 3000 Scrap; crafting it multiplies your score by 0.01. Jack's 55th Birthday: unlocked by a B rank in Guest House 2.