While Simon's whip is his primary weapon, sub-weapons are essential for overcoming specific challenges and bosses. Choosing the right sub-weapon for a given situation is your primary 'build' decision in Castlevania. Each sub-weapon consumes hearts, so managing your heart count is crucial. Experiment with each to find your preferred style, but some are objectively more powerful or versatile than others.

Sub-Weapon Breakdown:
- Dagger: Throws a fast, straight projectile. Low heart cost. Good for consistent damage at range, but often outclassed by other options.
- Axe: Throws an axe in an arc, hitting enemies above Simon. Moderate heart cost. Excellent for flying enemies, enemies on higher platforms, and many bosses (e.g., Death, Phantom Bat).
- Holy Water: Throws a vial that shatters on the ground, creating a flame pillar. Moderate heart cost. Incredibly powerful against ground-based enemies, Mummies, and especially effective against Dracula's forms. Can stun enemies.
- Stopwatch: Freezes all enemies on screen for a short duration. High heart cost. Situational but can be a lifesaver in crowded areas or for getting free hits on bosses. Use sparingly.
- Cross: A boomerang-like projectile that flies forward and returns. Moderate heart cost. Can hit multiple enemies on its path. Good for clearing horizontal lines of enemies.
For most of the game, the Holy Water and Axe are considered the strongest sub-weapons due to their utility against bosses and difficult enemy formations. The Dagger is a decent default, and the Stopwatch is a powerful emergency tool. Always try to have a sub-weapon equipped, as they provide crucial offensive and defensive options.