EX Mode
From Final Fantasy Wiki
EX Mode is a gameplay term from Dissidia Final Fantasy. EX Mode effectively serves as Dissidia's Limit Break system, granting the user an extreme boost in power. This grants access to new abilities, including the highly powerful EX Burst.
[edit] Entering EX Mode
To enter EX Mode, players must fill up their EX Bar located to the left of their health meter by collecting EX Force that appears when a player is hit by an attack, blocking an attack, other environmental hazards (i.e. spikes in the Pandaemonium and the fast gears in Ultimecia Castle in their Dynamic Version), or by pressing and holding 
if playing as Gabranth. The EX Bar can also be filled by collecting items called EX Cores, which appear in fixed spots for each arena, near the character with most Luck, and collects EX Forces around the arena to increase the portion of the EX Bar filled once obtained and changes in appearance depending on how much EX Cores it has collected. Once the EX Bar is full, the player can enter EX Mode by pressing the and R Trigger at once. Once EX Mode is entered, the EX Bar drains, and EX Mode ends when it empties, but collecting EX Forces and Cores will increase the duration of the Mode, and certain equipment also extends its time.
While in EX Mode, players are under the Regen status and will slowly regenerate health. Their appearance changes, they get a higher chance to get critical hits, they gain new abilities and their attack power increases, giving them stronger attacks they would normally not have access to. For example, several characters gain the ability to attack twice, while others have the range of their attacks increase. Entering EX Mode also cancels out any attacks the player is performing and any combos the opponent is striking them with, allowing attacks to be canceled out and chained in ways otherwise impossible. In this, EX Mode can easily turn the tide of a losing battle.
For most of Dissidia's playable cast, their EX Modes involve a transformation of theirs from their original game. For example, Sephiroth enters his "One-Winged Angel" form, Ultimecia fuses with Griever, Warrior of Light class-changes into his Knight form, Zidane, Terra and Kuja enter their variations of Trance, and so forth. The fighters who do not transform - Firion, Cloud, Squall, and Tidus, instead have their weapons transform into their ultimate weapons, such as Squall's Revolver into the Lion Heart or Firion's weapons into "blood" weapons.
[edit] EX Burst
During EX Mode, the player can execute an EX Burst, an extremely powerful attack that can inflict a great deal of damage to opponents. After connecting with an HP attack while in EX Mode, an icon appears on the screen. If is pressed again while the icon is visible the character will use their EX Burst. Once an EX Burst is triggered, there is a sequence in which the player charges up the EX Burst (the exact method varies for each fighter), followed by the attack executing. EX Bursts tend to be devastating, capable of depleting all of an opponent's HP. Once the EX Burst is executed, EX Mode is automatically canceled. If the player ends up falling victim to an opponent's EX Burst, the player can increase their Defense to reduce damage taken by continuously pressing 
at the same time as the opponent charges up the EX Burst to set the meter to +5 or +10 defense but if the player continues to press further, it might get to -5, decreasing it instead.
For the games in which the Limit Break system exists, EX Bursts are based on that character's Limit Break. For example, Terra uses Riot Blade, Cloud uses Omnislash, Squall uses Renzokuken, and so forth. For the characters from games that do not have a Limit Break system, their EX Burst is more original. Cecil's EX Burst involves magic and sword slashes, Bartz's revolves around his abilities as a Mime, etc. For the villains, some of their EX Bursts are either based on their strongest attacks, like Kefka's "Light of Judgment"/"Forsaken", or Cloud of Darkness' "Ultra Particle Beam", based on her "Particle Beam" move; or, in majority, entirely original, like Garland's "Soul of Chaos".
