Constitution, generally abbreviated as CON, is recurring a statistic featured in the Castlevania series. Most often, it is the character's "natural" defense, and their Constitution plus their armor's strength make up the Defense (DEF) stat proper.
Game specific information[]
Castlevania: Symphony of the Night[]
Constitution (CON) first made its debut with the role-playing game mechanics introduced in Symphony of the Night, along with Strength, Intelligence, Luck, Attack, and Defense. Ever since, it has been more or less a staple in "Metroidvania"-style games. It only improves for Alucard, though. As such, Richter Belmont and Maria Renard are more vulnerable in the realm of defense since they do not level up to increase their stats.
Alucard's DEF bonus given by his CON can be calculated using the following formula:
√[x + (y × 8)] - 2 = Base DEF
in which x is his natural CON and y is the bonus CON given by the equipment. In other words, take the y value and multiply it by 8, then add the x value (if the result of this is negative, replace it with 0). Take the square root, then subtract 2 and truncate the decimal. The result is the amount of DEF Alucard has due to his CON score.
So if his base CON is 81 and the bonus from the equipment is 20:
√[81 + (20 × 8)] - 2 = 13
his base DEF will be 13 (the decimals are truncated).
As can be seen by the formula, bonus CON from equipment is eight times more effective than base CON and, as such, makes a much more substantial contribution to the DEF stat. In the example above, 81 base CON accounts for a mere 3 extra points to the DEF stat.
CON also governs the duration of Poison and Curse status effects; as CON increases, the effect time decreases.
Castlevania: Circle of the Moon[]
The stat is unseen in Circle of the Moon and Harmony of Dissonance, although DEF replaced it for those games.
Castlevania: Aria of Sorrow[]
In Aria of Sorrow and the Nintendo DS games (Dawn of Sorrow, Portrait of Ruin, and Order of Ecclesia), for every 2 points of CON earned, the character gains DEF +1.
Specifically in Aria of Sorrow, in order to keep spikes always a threat to the player, they'll do more damage the higher their CON stat is. As such, removing equipped armor, removing any Enchanted Souls that boost CON (White Dragon, Quezlcoatl, Gorgon, Dead Crusader), as well as any Accessories that boost CON will greatly reduce damage taken from spikes, which can be useful for traversing areas filled with these environmental hazards (such as the pendulums room in the Clock Tower that leads to the Burtgang).