Status effects have always been a key part of all Final Fantasy games. Final Fantasy X has a similar set of status effects to other versions of the game, though modified slightly for the unique combat mechanics of this game. Positive status effects are generally reserved for boss battles in the early portion of the game since you don’t tend to have the magic points to spare on them and enemies don’t use them. Later in the game, you will use them more regularly, as will normal enemies. The following guide to positive status effects in Final Fantasy X will help you take advantage of the best effects and counter those effects on enemies when appropriate.
NulFrost / NulBlaze / NulShock / NulTide – These four effects are all one time shields against the appropriate damage type. They are rarely useful against standard enemies, but are particularly useful in boss battles and when fighting Aeons. Against Aeons, you can usually tell exactly what damage type that Aeon will use, which means that these effects can make you practically invulnerable in some battles. If an enemy uses this effect, it is usually more effective to cast a weak elemental spell that breaks it, rather than use a Purifying Salt to remove it.
Haste – Haste roughly doubles the speed at which the character acts. Tidus will practically start the game with the ability to grant this effect and you can grant it to your whole team if you learn the Hastega spell. Bosses use this effect regularly and you can either counter it with Slow or with a Purifying Salt.
Protect – Protect is another effect that bosses will use regularly. A character affected by Protect takes half damage from physical attacks. If you have the ability to attack only with spells, you can completely ignore this effect on enemies if you want. This is rarely needed in most normal battles, since a single healing spell will generally provide the same effects as a Protect effect, but it is very useful in many boss battles. You may use it more regularly later in the game when battles last longer. A Purifying Salt or a Dispel will remove this from an enemy.
Shell – Shell does for spells what Protect does for physical damage. This is often much more important in the early game than Protect, because spell damage is more likely to be higher when you face it. Against enemies like Aeons where you can identify the damage type the enemy will use, one of the Nul status effects works better. But against enemies that don’t have a clear damage type, use Shell to protect your party.
Reflect – Reflect is a beneficial effect that you want to be prepared to remove from your own party. Some enemies will actually cast it on your party to try to prevent you from healing your party and you may occasionally cast it on an enemy for the same reason. Normally, though, this effect is the universal solution to a spell casting enemy. Spells cast at a Reflect will bounce back at the caster. You need to heal with items while a Reflect effect is active, but if you use it right, you probably won’t need to heal at all.
Regen – Regen is the exact opposite effect of Poison. The target heals 25% of total hit points every turn. When combined with Haste, the target heals at an amazing rate. This is a simple and effective way to preemptively counter a Poison effect and is generally better to cast on an ally before the ally takes damage, even if some of the healing is wasted. It is not particularly safe for healing after damage is taken because it takes a while to fully heal someone. When an enemy uses this effect, you remove it with a Purifying Salt or cast Bio on the enemy to effectively negate the effect.