There are various combat mechanics in Dissidia Final Fantasy Opera Omnia that may need explanation, as the game is in Japanese and so they aren't all immediately obvious. Caution: All of the following are subject to change upon further updates, so stay tuned.
Easily the most basic kind of attack in this game, Brave Attacks reduce targets' Brave depending on user's Attack and refill the user's Brave by same amount. Reducing enemy's Brave below 0 will trigger Break status (see below)
Abilities that do Brave Damage are signified by "BRV" icon on top left of the button.
HP Attacks spend all remaining Brave Points to deal damage to target's HP. If target's HP reaches 0, it gets KO'd and loses its ability to fight. Note that HP Attacks will do nothing to Brave Points and vice versa, nor does Brave Points provide any protection against HP Attack.
Abilities that do HP Damage are signified by "HP" icon on top left of the button. Some abilities that include BRV attack (e.g. Cloud's Cross Slash) are still classified as HP Attacks since their final strikes do HP Damage and thus deplete remaining Brave.
If the target can be finished by HP Attack on that turn, the button (or the Brave Points, in case of enemies) will glow with purple aura.
Damage types determine how effective/ineffective attacks and abilities will be against certain enemies.
- Melee: Signified by Sword icon. Treated as Physical for resistance.
- Ranged: Signified by Shuriken/Gun icon. Treated as Physical for resistance.
- Magic: Signified by glowing Orb icon. Treated as Magical for resistance.
If the damage done to target's Brave is larger than target's current Brave, the target enters Break status for certain number of turns. Broken target can still be hit by Brave Attacks, but this will not keep the target's Brave at 0; instead, its Brave slowly regenerates per turn independently. Gaining Brave by attacking will still work, and recovering Brave above set amount will free the character from Break. (Note: If CPU recovers from Break status with its Brave filled high enough, it will almost definitely use HP Attacks unless it has scripted move. This can be extremely frustrating in boss fights, so one should always watch when it will actually recover from Break and plan accordingly. The pattern can be exploited to avoid getting Broken by tricking enemies into using HP Attacks instead of Brave Attacks - mainly for scoring Complete in Dailies/Event Missions - but generally is not worth the risk.)
Breaking will award all enemies/allies certain Brave Points which equals the "Break Bonus" displayed on top of the screen divided by number of party members. Because of this, Break Bonus can be extra game-changing when fighting a single boss, since any ally Broken will lead to the boss' Brave literally skyrocketing in one move.
Break Bonus is only awarded when the target is broken for the first time; enemies/allies being Broken by multi-hit moves or multiple breaks happening due to AoE will still count as one Break.
Note that using HP Attack depletes all Brave Points of the user, which means that using HP Attack right before enemy's turn might put the user at risk of being Broken. Same applies for enemies, and can be used to advantage.
Under Auto Mode, the CPU will prioritize in Breaking enemies even though HP attacks can KO the enemy faster.
Sometimes allies' attack send enemies flying (some abilities, like Cloud's Finishing Touch, can do this at will). If enemies hit the wall they will suffer extra damage in Brave/HP.
And sometimes allies will chain in their attacks midair, thus is called Chase Mode. Allies can chain in either Brave/HP Attack depending on their situation. If no move is chained within 5 seconds, the game will automatically use Brave Attacks. It can also be manually cancelled pressing Cancel button (large X mark, appears right above the Summon button).
Quite obviously, character-specific Abilities cannot be chained in.
If the enemies can be blown away, small icon resembling flipping arrow will appear upon being targeted. Since attacks by Chase do not spend the turn of those participating in Chase and do not count toward the total Turn count, every chance for Chase is worth it.
Detailed conditions for triggering Chase are unknown, yet the game's tutorial states that "the more attacks are focused on one enemy, the more likely Chase will trigger."
Sometimes, attacks can be dodged. This is caused by either enemy buffs (e.g. Flap ability used by Bats) or intrinsic evasion rate (e.g. Cactuars).
Failing to land HP Attack will deplete the user's Brave, and it will deplete Ability uses.
Players can evade enemy Brave/HP attacks via skills that can blind (Vaan's Luminescence), and can evade status effects.
Turn order is determined by characters' Speed status. Also, there is separate stat for each Ability called "Delays (行動負荷, literally translates to "Burden after Acting")" that affects the Turn Order after using the Ability. Some passives can reduce such Delays.
Breaking the enemy will push its Turn order back by 1. Enemies such as Bats, Skeleton and Magitek Armor, upon being Broken, will be immobilized and skip a whole turn (i.e. can act after all allies have acted at least once).
Some abilities (like Stone magic) can delay enemies'/allies' turn at will.
During the battle, the Summon gauge at the lower right of the screen will fill up. When it is filled completely, Summon will become available.
Summoning will call an Esper of choice to deal powerful Brave damage to all foes, and grant allies extra turns (2 per character) and boost in maximum Brave. Some Espers have unique buffs that affect the allies' Brave Attacks.
Turns taken during Summoning Mode does not count toward total Turn count. However, status ailments timer will not stop during Summoning Mode, which makes Summoning while debuffed generally a bad move, unless used in really urgent situations.
If enemy targets an ally for its next turn, it will be indicated by the character's portrait, or letters in case of targeting enemies themselves.
The enemies Brave Points are indicated by numbers above them. Brave Attack and Breaking mechanics work in same way as allies'.
Enemies have resistances/weaknesses of their own, and resistance halves the damage of Brave Attack of corresponding type. If attack is resisted, "DEFENCE" will appear along with the damage number. If attack is effective, "WEAK" will appear. The resistances can be checked from the Enemy Info (the rightmost tab in the window at lower right of battle preparation screen). For elemental attributes, blue letter(弱) means weakness and red letter(耐) means resistance. However, physical/magical resistance are not displayed and must be figured out from the texts.
For instance, Flans are weak against Fire attacks, and resistant against any physical attacks, melee and ranged alike (needs to be checked what happens when hit by Fire-elemental Physical attack).
Aside from intrinsic resistance, some abilities (Hope's Shell/Protect, Skeleton's Brace) can bestow resistance against certain attack types during battle.
Resistances have absolutely no effect on HP Attacks.
Monsters in DFFOO have loose categorization, and even lookalikes have different abilities. Therefore, while it is able to guess monsters' ability by their looks or trial and error (e.g. Wolf Leaders will always use Shout on their first turn, Bombs will use Self-Destruct when critical HP, etc.), it is important to look up for info every time you encounter a new kind of enemy.
Still, some passives allow characters to deal extra Brave damage to certain "Types": Zidane's Wolf Killer (bonus against Wolves), Tifa's Skeleton Slayer (bonus against Skeletons), and Steiner's Human Slayer (bonus against Humanoids, including Imitations) are good examples. While the codex does not reveal what "Types" the enemies fall into, such "Types" are easily discernible by looks.