Final Fantasy XIII/Roles

You are able to research different roles in the ../Crystarium/, with certain roles being available earlier for different characters. Each role has a number of abilities to make your character more effective. Depending on the character's stats, including boosts from weapons and accessories, and the abilities available to them, certain people are better suited for specific roles. When choosing roles for your characters, keep in mind their stats, available abilities, who they'll be partied with and their roles (for efficient paradigm decks), and your long term goals.

Commando
Commandos are the heavy hitters of the game. They do great amounts of damage and have abilities to interrupt enemy attacks and knock them into the air so they're immobilized. The Commando's greatest asset is strength, and in this department Fang is the best. Snow is also very strong, as is Lightning, but the former has one less ability than Fang and makes a better Sentinel, and the latter is much weaker and missing even more Commando abilities. Besides their great attack power, Commandos can slow down the rate that an enemy's chain gauge depletes and they direct Ravagers so their attacking the enemy. The combination of Ravagers and a Commando, quickly boosting up the chain gauge and then slowly its decay, respectively, is the most reliable way to stagger an enemy. Commandos mainly use physical attacks, and will move to far away or moving targets, though they do have the option to use Ruin if an enemy is airborne, moving too fast or resistant to physical attacks.

The Commando's job is a simple one compared to some of the other roles, so it's a great role to give the party leader, as that's one you'll be controlling. The AI does exactly what you would do as a Commando using the auto-attack option. A good pairing with a Commando is a Sentinel who will keep the attacks away from you, freeing you to do as much damage as possible without being interrupted.

Medic
Medics have the simplest jobs of any role—just restore allies' health or bring them back to life if they get knocked out. Unless you're fighting very strong opponents, try to use paradigms with Medics in them as little as possible so you can keep inflicting damage. You'll also want to be careful to switch out of a healing paradigm quickly if everyone is fully healed with no status ailments, as the AI Medic will just sit there doing nothing. Both Hope and Vanille can perform all Medic abilities, and they both have excellent magic stats, so are the best suited for the job. If one of them isn't available, try to use Lightning or Fang in this capacity, as they are the other characters that can use Raise. The effectiveness of a Medic's abilities is based on their role level and magic stat.

The AI Medic will attempt to heal allies with health bars in the red before ones in the yellow, and ones in the yellow before ones in the green. If all else is equal, the Medic will attempt to heal the party leader first, then themselves. They will also heal low health first, then raise knocked out allies, then remove status ailments. In some cases it is better to use a Synergist to cast the opposite of a status ailment on an ally rather than waiting for the Medic to use Esuna. The nice thing about using the AI Medic is that they will automatically use the least expensive spell to get the job done. In other words, they'll use one ATB segment of Cure if that's all it takes.

Ravager
Ravagers are an essential part of building an enemy's chain gauge up. They rely mostly on magic attacks, with the exception of the "strike" abilities and the unique abilities like Army of One, Cold Blood and Last Resort. Because this role is based heavily on the magic stat, it's good to research this role with a character that has high magic and is also researching another magic-based role like Medic, Saboteur or Synergist. Characters in those roles usually don't stay in them exclusively, so you'll want a damage-dealing role for the paradigms you switch to between them. For the pure Ravager specialist, Lightning is your best choice. Not only does she have access to nearly all the Ravager abilities, but she has very high magic and strength, though not enough to be the best Commando or Sentinel. Hope is another good choice, as he has the area-of-effect spells Lightning is missing and tons of magic.

When the AI plays the Ravager role, it will target whichever enemy you're targeting as the leader to quickly build up its chain gauge. Because the Ravager's abilities are mainly status-based, you'll want to make sure your enemies are scanned so the AI can queue up the proper attacks. A Synergist can greatly boost the efficiency of your fights by buffing a Ravager's status attack even further against an enemy already weak to that status. In addition to Ravagers in your party, you'll also want to have either a Commando or Saboteur to slow down the decay on enemies' chain gauges.

Saboteur
Saboteurs are on the other end of status effects from Synergists—instead of casting buffs on your party, a Saboteur will cast debuffs on enemies. Like all roles that involve status effects, it is very important to know the enemies' status weaknesses, resistances and attacks. In addition to debuffing the enemy, the Saboteur's abilities also inflict some magic damage and maintain the chain gauge like a Commando. The later effect is essential when you're lacking a Commando in your party to slow down the chain gauge's decay, or your Saboteur is also your Commando. Characters' access to abilities is all over the board, so you may want to train two complementary characters to have access to all the abilities. Vanille and Fang are great choices, as they start with the Saboteur role, they have different sets of abilities and Vanille is the only one that can cast Death.

Because it's complicated to try and figure out the status information yourself during battles, relying on the AI Synergist is advantageous, as it automatically chooses debuffs based on the enemies' weaknesses and attacks. Besides casting spells to reduce an enemies resistance, Saboteurs can also remove enemy status enhancements. It is also good to train characters in this role as Ravagers, as that is also a magic-dependent role and you'll want to be able to inflict damage after switching paradigms when the enemy is full of status ailments.

Damage and chance of success for the Saboteur's abilities is based on a formula which modifies the base percentage of a given ability. In the table below, the base percentage rate of success is given, but you can increase the chance of success dramatically by influencing certain factors. The success rate is modified by the enemy's susceptibility to the status ailment, the current chain percentage, whether Vigilance has been cast on the Saboteur, the Saboteur's role level, whether the enemy is using Veil and any Improved Debuffing or Improved Debilitation properties on the Saboteur's weapon.

Sentinel
Sentinels won't seem very useful until you've leveled them up fairly high and have a lot of HP to expend. At earlier parts of the game, the Sentinel won't do much with the auto-attack except Provoke and Steelguard. Later though, this role becomes essential to draw fire away from vulnerable allies, allowing your party to either recover or inflict damage on a tough enemy without having to stop to heal. At very high levels, Sentinels can absorb huge amounts of damage and counter automatically, basically freeing you up to do anything from heal, attack, buff or debuff. The Sentinel's most important stat is HP, and Snow has the greatest potential for growth in that area. He also has access to the most abilities of any character except Fang, who has the same ones but lower HP.

As your main abilities are percentage-based, it's best to queue up multiple segments of a single ability to stand the best chance of success. Like Commando, this is a fairly simple role and a good one for the party leader so you can control the character. This has the added benefit of being able to direct your Challenges to higher priority enemies that the AI Sentinel might not pick.

Synergist
Synergists have the ability to buff party members through status enhancements. Generally, it's best to use paradigms with a Synergist at the beginning of a battle to take advantage of the boosts for the longest amount of time. Status enhancements are only active for a limited time, so you may need to refresh them during longer fights. You can see the icon corresponding to the status on the left side of the character's health bar. Sazh is a great character for the Synergist role, as he has access to most of the abilities, including the important ones, and his stats aren't so great that you'll be missing him in another role. Boosting his magic stat to take full advantage of the role will also help him as a Ravager for when you switch paradigms when you no longer need status enhancements.

Like all roles involving status effects, it's very important to know your enemy's weaknesses, resistances and attacks. The AI Synergist is great, as it automatically queues up buffs based on what your enemy will be attacking with and what it is weak against, while avoiding useless buffs. Doing this yourself can be time-consuming if you have to constantly switch to the enemy info screen and try to decipher what will work yourself. If you know you'll be wanting a specific spell cast that the AI normally doesn't do, such as Veil or Vigilance, then you might want to control the Synergist yourself to cast them at the beginning of the fight.