Knife

Sub-weaponナイフ

Flies straight ahead; fast but weak. Disappears when it hits an enemy or a wall.

Second line: Shooter mode values

Heart cost: 1; 1
Multiplier: ×0.45; ×1.41
Power: 20%; 199%
Max / Doubled: 3 / 6

ATK = STR × multiplier, power = multiplier² (same as DSS: damage ≈ normal whip damage × power).

Max: how many can exist at the same time. Doubled: the max with the DSS combo Doubled Sub-Weapon (Pluto + Serpent) active. The same applies in Shooter mode.

Homing Knife

Shooter mode only: picking up a knife while holding one upgrades it to a knife that homes in on enemies.

Heart cost: —; 1
Multiplier: —; ×1.26
Power: —; 159%

How to obtain

Show on map (32 spots)

Found in the castle: Catacomb — candle 5
Found in the castle: Abyss Stairway — candle 2
Found in the castle: Audience Room — candle 4
Found in the castle: Outer Wall — candle 1
Found in the castle: Machine Tower — candle 4
Found in the castle: Eternal Corridor — candle 1
Found in the castle: Chapel Tower — candle 3
Found in the castle: Underground Gallery — candle 5
Found in the castle: Triumph Hallway — candle 1
Found in the castle: Underground Warehouse — candle 3
Found in the castle: Observation Tower — candle 2
Found in the castle: Battle Arena — candle 1

Notes

If you already carry the same sub-weapon, the candle drops a large heart instead (except in Shooter mode with the normal knife, where it still drops the knife so it can become the homing knife; once you have the homing knife, it drops a large heart).