Critical ability

SOS Abilities are a set of recurring abilities in the series. First appearing as SOS Shell in Final Fantasy V, SOS abilities have grown to include just about all of the positive Status Effectes, and are only active so long as the user is in HP Critical. The SOS ability cannot be Dispelled while active, and will automatically reapply itself should the character be KO'ed and revived back into Critical. The moment the user is restored to above their Critical HP limit, the ability will wear off.

The following is a list of SOS abilities that have appeared throughout the series:
 * SOS Shell (aka Magic Shell) - Automatically puts the user in Shell status.
 * SOS Protect - Automatically puts the user in Protect status.
 * SOS Haste/Last Haste - Automatically puts the user in Haste status.
 * SOS Wall - Automatically puts the user in Protect and Shell status.
 * SOS Reflect - Automatically puts the user in Reflect status.
 * SOS Regen - Automatically puts the user in Regen status.
 * SOS NulBlaze - Automatically puts the user in NulBlaze status.
 * SOS NulFrost - Automatically puts the user in NulFrost status.
 * SOS NulShock - Automatically puts the user in NulShock status.
 * SOS NulTide - Automatically puts the user in NulTide status.
 * SOS Overdrive - Increases Overdrive gauge gain.
 * SOS Spellspring - Reduces cost of spells and techniques to 0.
 * SOS Critical - Always deal Critical Hits.
 * SOS ???? - As long as the user is in Critical, all healing items and spells heal for 9999 and all damage attacks, spells, and items will deal 9999 per hit.

While the following aren't named "SOS", they still follow the same format:
 * Adrenaline - Doubles attack.
 * Last Stand - Doubles defense.
 * Spellbreaker - Doubles magic.
 * Chivalry - Increases Attack and Magic.
 * Gallantry - Increases Defense and Magic Defense.
 * Restore HP/Critical: Recover HP - Regains half of Max HP/HP if character survives an attack while in Critical.
 * Last Berserk - Automatically puts the user in Berserk status.
 * Critical: Recover MP - Regains MP.
 * Critical: Quick - Can attack quicker.
 * Critical: Vanish - Automatically puts the user in Vanish status.
 * Critical: Evasion - Increases Evasion.

Final Fantasy IV
Adrenaline and Last Stand appear in the Nintendo DS version of the game only as Augments. Adrenaline is received through Cid after modifying the Falcon and by giving him 2 Augments. Last Stand is received at the Tower of Zot, and if Tellah had been given 1 or more Augments.

Final Fantasy V
Magic Shell, also known as Magiwall or Barrier, is the Level 1 ability of the Mystic Knight class. It requires 10 ABP to learn, and once mastered, will automatically activate Shell when in Critical if the character is a Freelancer.

Final Fantasy VI
The Barrier Ring cast Shell while the Mythril Glove cast Protect on the user once they enter Critical status. The Princess Ring, a female-exclusive relic, casts both Protect and Shell when the user is Critical. There is a dummied ability that cast Reflect when the user came under the Critical status.

Final Fantasy IX
Restore HP ability can be learned by the melee characters through the Brave Suit, Promise Ring, Platinum Helm, Grand Armor, and Minerva's Plate.

Final Fantasy X
There are numerous SOS abilities in Final Fantasy X. The SOS Overdrive ability is an auto ability for weapons. It is the SOS version of Double Overdrive, charging the Overdrive gauge at double the rate when the character's HP is HP Critical. It can be customized to a weapon with 20 Gambler's Spirit items.

The SOS abilities for armor focus on granting a status to casters. Each of the four elements have their own respective SOS ability which provide completely immunity from an element when the character with the respective equipped armor via the Nul- statuses. Due to their functionality, they work like SOS versions of the elemental "proof" abilities. The SOS NulBlaze auto ability grants the user the NulBlaze status, giving them full immunity to the Fire element as long as their HP is critical, and can be customized to an armor with a Bomb Core item.

The SOS NulShock auto ability grants the user the NulShock status, giving them full immunity to the Lightning element as long as their HP is critical, and can be customized to an armor with a Lightning Marble item. The SOS NulTide auto ability grants the user the NulTide status, giving them full immunity to the Water element as long as their HP is critical, and can be customized to an armor with a Dragon Scale item. The SOS NulFrost auto ability grants the user the NulFrost status, giving them full immunity to the Ice element as long as their HP is critical, and can be customized to an armor with an Arctic Wind item.

The remainder of the SOS abilities for armor are all spiritual predecessors of a number of the abilities with an "Auto-" prefix. The SOS Shell auto ability grants the user the Shell status as long as their HP is critical, and can be customized to an armor with eight Lunar Curtain items. The SOS Protect auto ability grants the user the Protect status as long as their HP is critical, and can be customized to an armor with eight Light Curtain items.

The SOS Reflect auto ability grants the user the Reflect status as long as their HP is critical, and can be customized to an armor with eight Star Curtain items. The SOS Haste auto ability grants the user the Haste status as long as their HP is critical, and can be customized to an armor with 20 Chocobo Feather items.

The SOS Regen auto ability grants the user the Regen status when their HP enters critical. Unlike other SOS abilities, it remains with the player after they have left the Critical status, however it becomes susceptible to Dispel. It can be customized to an an armor with 12 Healing Spring items. Customizing SOS Regen to armor is part of a Gil trick involving Kottos at the Monster Arena.

Final Fantasy X-2
SOS Shell, Protect, Regen, Wall, Haste, Spellspring, and ??? are the SOS abilities in Final Fantasy X-2. All but SOS ??? can be found on various Dresspheres, while SOS ??? is unique to the accessory Cat Nip. SOS Critical is unique to the Samurai, and costs 80 AP to master as well as having already learned Fireworks. SOS Shell is an ability of the Selene Guard Garment Grid.

Final Fantasy XII
Adrenaline, Last Stand, and Spellbreaker are all SOS abilities found in Final Fantasy XII. which increase attack power, defense and spell power, respectively. Adrenaline and Spellbreaker take 65 LP to learn, while Last Stand takes 70 LP. The same effects can be gained via certain accessories.

Final Fantasy XII: Revenant Wings
Gallantry and Chivalry are SOS abilities exclusive to Basch.

Final Fantasy XIII
Critical: Protect, Shell, Veil, Bravery, Faith, Vigilance, Barfire, Barwater, Barfrost, Barthunder, Haste and Tetradefense are gained by equipping certain accessories.

Critical:Shell is granted by the Auric Amulet.

Final Fantasy Tactics
Critical: Recover HP, also known as HP Restore, is a reaction ability in Final Fantasy Tactics. The Monk class learns it for 500 JP. When a unit equipped with this ability suffers from critical loss of HP, the unit's health will be replenished automatically.

Critical: Quick is a reaction ability in Final Fantasy Tactics. The Time Mage class learns it for 700 JP. When a character receives damage that reduces his/her HP to critical level, the character's AT will be elevated into the next position for immediate turn. This ability is the basis of the Quickening Glitch, which allows player's characters to act infinitely.

MP Restore is a reaction ability in Final Fantasy Tactics. The Summoner class learns it for 400 JP. If this unit is attacked and put into a critical state, this ability will activate, fully restoring the character's MP.

Final Fantasy Tactics Advance
Last Berserk is learned from the Defender job for 300 AP, while Last Haste is learned for 300 AP from the Beastmaster, Ninja, and Mog Knight classes. Last Quicken is also learned for 300 AP, from the Time Mage.

Final Fantasy Tactics A2: Grimoire of the Rift
SOS abilities include Critical: Haste, Critical: Quicken, Critical: Vanish, Critical: Berserk, and Critical: Evasion↑.

Dissidia Final Fantasy / Dissidia 012 Final Fantasy
The abilities Magic Shield and Physical Shield activate when the character is at critical HP, and reduce magical and physical damage by 20%, respectively. The Back to the Wall ability increases the chance of landing critical hits by 50% when the character is at critical HP, while Cat Nip increases the chance by 50% when the opponent has enough Bravery to kill the character in one hit.

The Rebellious Soul carries the Bonecrusher ability, which increases the character's Bravery by 20% of their max HP when they enter critical health. In Dissidia 012 only, the Fury of Qu'bia accessory found only in the Labyrinth carries the same ability.

Etymology
SOS is the commonly used description for the international Morse code distress signal (· · · — — — · · ·). In popular usage, SOS became associated with such phrases as "save our ship", "save our souls" and "send out succor".