Gau is a playable character in Final Fantasy VI. As a Feral Child, Gau fights by mimicking the behavior of monsters, allowing him to use a wide variety of attacks, but doing so puts him into a berserk-like state when he becomes uncontrollable and acts on his own.
Gau's stats are all around high. His Strength is the third-highest in the game and his Speed, Stamina, and Magic are above average. He has the second-best Evasion after Shadow and the best Magic Evasion. His only stat that is lacking is his Defense, which is mediocre, but Gau has access to the most physically defensive armor in the game, covering for this shortcoming.
To compensate for his inability to equip a weapon, Gau's natural attack power is much higher than any other character's—his base Battle Power is 99, when most characters don't exceed 20.
Gau is unique among the party in that he cannot equip weapons, save for the universal Impartisan that has low battle power unless he's under the Imp status. Despite this, the Impartisan does have an important use for how it interacts with Gau's relics.
Gau's armor options are limited to lightweight gear. Because he lacks an ultimate weapon obtainable in the Dragons' Den, Gau has an "ultimate armor" instead, the Dueling Mask, which increases all his stats by 6, his HP by 25%, and halves elemental damage.
Gau is one of three characters able to equip the Snow Scarf, the best armor in the game with Defense and Magic Defense surpassing all other armor save for the Reed Cloak, which is only active under Imp status and only trumps the Snow Scarf by 10 Magic Defense. With the Snow Scarf and Dueling Mask, Gau is the bulkiest character in the game even before additional benefits from a shield are taken into account.
Three relics of note for Gau are the Genji Glove, the Gauntlet, and the Master's Scroll. The effects of these relics affect not only Gau's normal attacks, but also special physical attacks, such as Cat Scratch and Critical. The Genji Glove and Gauntlet only take effect if the user is equipped with a weapon, which is where the Impartisan has utility for Gau since it is the only weapon he can use. With these relics, Gau's physical attacks can hit twice, deal additional damage, or hit four times.
Gau's special ability is Rage, which lets him mimic the behaviors of monsters. When fighting on the Veldt, Gau has the Leap command whose use instantly ends the battle and removes Gau from the party. A time later when fighting on the Veldt, Gau will reappear at the end of a battle and, if not attacked, will rejoin the party having learned the Rages of any enemies that were in the enemy formations when he Leapt and when he returned.
When Gau uses a Rage, he takes on that enemy's elemental and status affinities, including innate statuses and immunity to statuses. This includes statuses that normally cannot be afflicted on the party: undead and dying at 0 MP. The latter only occurs if Gau's MP is reduced to 0 while under Rage; if his MP is already 0, he will be unaffected until an attack damages his MP. Each individual elemental affinity of a Rage will overwrite Gau's affinity to that element only if his equipment offers inferior protection—an enemy that is immune to fire-elemental damage would overwrite resistance to fire, but not absorption.
While in Rage status, Gau becomes uncontrollable and will randomly perform a normal attack or a special attack each turn, with a 50% chance of either. Rage continues until Gau is KO'd, petrified, or until the battle ends. If Gau is KO'd and revived, the elemental and status affinities of Rage will not persist, with the exception of Float.
Gau's Rages make him perhaps the most powerful character available in the World of Balance. He can access tier-two magic spells well before the party gains access to magicite, and can perform powerful physical attacks. Later in the game Gau can easily access earth, water, and wind spells, elements not easily available to other party members, and he can cast top-tier magic, including Meteor.
However, Gau's viability in the late game suffers due to his uncontrollable nature—while he can use powerful abilities, other party members can perform similarly and do so reliably without giving up player control. Gau's Rages do not become useless, but using him can be risky if the player needs a party member for a different task than what his current Rage locks him into doing.
Two popular Rages for Gau are the Stray Cat and Magic Urn. The Stray Cat's special attack, Cat Scratch, is a powerful Level 6 attack. While other Rages can be more efficient under various circumstances, the Stray Cat Rage is a simple but powerful option that can carry Gau through the game comfortably, as it can deal several thousand damage and even hit the damage cap as Gau trains up his Strength. Magic Urn absorbs all elemental damage and its special attack is Curaga, which, supplemented by Gau's powerful equipment, makes him very durable and allows him to support the party with healing magic.
"Wind God Gau"
A particularly powerful strategy for Gau was so effective that it was removed from all versions of Final Fantasy VI after the original Super NES release. Equipping Gau with the Merit Award allows him to equip the Kazekiri ("Tempest" in the Super NES translation), which has a chance to cast Wind Slash when attacking. The coding to randomly use Wind Slash is identical to the coding for casting spells when attacking that other weapons have, but is a separate mechanic, and because of this it is not disabled when using the Master's Scroll.
With this combination and the Stray Cat Rage, Gau will attack four times every turn, and each attack has a chance to use Wind Slash. Further, if Gau uses Cat Scratch, his attacks will be much stronger and the Wind Slash cast from them will also be more powerful. This allows Gau to reliably hit all enemies for maximum damage, potentially multiple times each turn. The only drawback is that the strategy is much less effective against enemies that are immune to or absorb wind-elemental damage, but very few enemies in Final Fantasy VI are. This strategy was nicknamed "Wind God Gau" by the fanbase.
The PlayStation Anthology release made Gau unable to equip the Merit Award, but the "Wind God Gau" strategy was not entirely gone, as Gogo could also do it, just less effectively since they have poorer stats and cannot equip magicite for level up bonuses to their Strength. The Game Boy Advance version made both Gau and Gogo unable to equip the Merit Award, and the mobile and Steam versions retain this.
Gau can be encountered as an "enemy" on the Veldt if he had Leapt previously and not returned yet and the party has fewer than four members. As long as the battle is not a back attack, side attack, or pincer attack, there is a chance Gau will appear after the monsters are defeated. He can be attacked and even killed during this time, but if the player does not attack him, he will speak up and rejoin the group with the Rages of any monsters present in the battle he leaped and the battle he returned in.
Gau is recruited in the World of Balance by purchasing dried meat from Mobliz and then using it on Gau in battle when he appears. After a cutscene, he will join. When Gau uses Leap to leave the party, he will eventually appear at the end of a battle on the Veldt and rejoin as long as the party has an empty slot for him. He will not appear if the party is full.
In the World of Ruin, Gau will appear at the end of battles on the Veldt as if he had used Leap and rejoins the party as he would normally.
Gau has unique dialogue when meeting Ramuh in Zozo, but because the game checks for his presence last when determining what dialogue to display, his unique dialogue will only trigger if he is the only party member.
In the World of Ruin, taking Gau to the house on the Veldt with at least him and Sabin in the party leads to a series of cutscenes where Sabin deduces the old man living there is Gau's father and dresses him up to introduce them. Completing this quest does not have any gameplay impact or rewards.
When Gau is Leapt on the Veldt, including the start of the World of Ruin, his levels are not included in the algorithm that calculates the levels of new and rejoining party members based on the average level of the currently recruited party members. This gives Gau important utility in low-level playthroughs as there are many scripted battles and unavoidable battles that reward experience points. To keep the party's levels as low as possible, players can fight these battles with Gau, allow him to level up, and then Leap him onto the Veldt so his level will not be included when determining the levels of newly joining characters.