Meet the criteria to unlock these weapons. They may appear as weapons for newly generated characters.

Weapon	How to unlock
Bone Dagger	Complete 3 levels in Pacifist mode on a single run.
Crossbow	Purchase 5 Unlocks.
Infinity Sword	Complete the game three times.
Katana	Purchase 50 Unlocks.
Musket Gun	Get a score of 25,000 in New Game Plus.
Pickaxe	Purchase 20 Unlocks.
Reaver	Kill 150 enemies on a single run.
Warhammer	Complete the game on Normal.