Dualcast

Doublecast, also known as X-Magic, Dualcast or Double, is a recurring ability which allows a character to cast two spells in one turn.

Final Fantasy IV
Doublecast appears as a Augment Ability in the Nintendo DS version. You obtain it by speaking with the Mysidian Elder only when you teach a total of three abilities between Palom and Porom before they leave the party, with each twin having at least one ability each.

Final Fantasy V
Dualcast is the Level 4 ability of the Red Mage.

Final Fantasy VI
Dualcast, also known as X-Magic, can be used if a character is equipped with the Soul of Thamasa Relic. The only drawback is that the character cannot summon the Esper he or she currently has equipped. By combining the Relic with the Quick spell, the equipped character can effectively cast five spells each turn.

Final Fantasy VII
The W-Magic Materia allows a character to cast two spells in one turn.

Final Fantasy VIII
The Double spell inflicts the status effect Double which allows characters to temporarily cast two spells at once. The Triple spell inflicts the status Triple which allows characters to temporarily cast three spells at once. Cerberus casts both on the party

Final Fantasy IX
When Vivi goes into Trance, he can use Double Black; cast two Black Magic spells in one turn. When Eiko Trances, she can use Double White; cast two White Magic spells in one turn.

Final Fantasy X
Doublecast only allows a character to cast two Black Magic spells in a row. It is located in Lulu's section of the Sphere Grid, but several locks must be passed first.

Final Fantasy Tactics Advance
Doublecast is learned by Red Mages via the Madu. When used, it allows the unit to cast two spells from both of the A-Ability sets if possible. Doublecast works with White, Black, Summon, and Spirit Magic. Doublecast can also be used to avoid some elemental, skillset, and Dmg2 laws because Doublecast is seen by the game as a non-aggressive, non-elemental, Red Magic ability. It is also one of few abilities in Final Fantasy Tactics Advance to cost 999 AP to master.

Final Fantasy Tactics A2: Grimoire of the Rift
Doublecast is again learned by the Red Mage for 999 AP via the Madu rapier. The game mechanics for it have changed, though; it is more sensitive to laws than its incarnation in Final Fantasy Tactics Advance. Though specific skillset laws have been abolished, the spells used in Doublecast will be sensitive to elemental laws.