The Psycho Cyan bug is a bug Final Fantasy VI. It is actually the combination of two bugs involving the Bushido technique Sky. The first bug allows Cyan to counter any physical attack dealt by any target if he is KOed and revived while in "Sky" status. The second bug occurs when Cyan is Imped while in "Sky" status. He counterattacks with a simple physical attack instead of Sky itself while Imped, and as such, "Sky" status never comes off. When these two bugs are combined, Cyan enters an infinite loop of attacking his opponents. Because he is imped, "Sky" status never comes off, and because he was revived after being KOed, he effectively attacks, and counter-attacks his own attack with another attack. The loop ends when all enemies on the screen are dead.

This bug was "fixed" in Final Fantasy VI Advance. However, it can still be done, albeit in a different way. First Cyan has to die. After being revived Cyan must perform Sky and if he is imped at this point he will go "Psycho Cyan." There is a bugfix patch that players can use to fix it on the SNES version, which fully corrects the bug unlike in the Advance version.

v · e · d Final Fantasy VI
Characters
Player characters Terra Branford - Locke Cole - Edgar Roni Figaro - Sabin Rene Figaro - Shadow - Cyan Garamonde - Gau - Celes Chere - Setzer Gabbiani - Mog - Strago Magus - Relm Arrowny - Gogo - Umaro
Temporary player characters Biggs and Wedge - Ten Moogles - Banon - ????? - General Leo Cristophe
Gestahlian Empire Emperor Gestahl - Kefka Palazzo - Cid Del Norte Marquez
Other characters Arvis - Baram - Crimson Robbers - Darill - Dream Stooges - Duane and Katarin - Duncan Harcourt - Elayne and Owain - Elder of Narshe - Esper Elder - Gau's Father - Gungho - Impresario - Interceptor - Lola - Madeline - Maduin - Mayor of Thamasa - Owzer - Rachel - Ramuh - Siegfried - Typhon - Ultros - Vargas - Yura
Locations
World of Balance - World of Ruin
Figaro-Narshe Region
Narshe - Narshe Mines - Figaro Castle - South Figaro Cave - South Figaro - Duncan's Cabin - Mt. Kolts - Sabre Mountains - Returner Hideout - Lethe River - Ancient Castle - Yeti's Cave
Doma-Mobliz Region
Gau's Father's House - Imperial Camp - Doma Castle - Phantom Forest - Phantom Train - Baren Falls - Veldt - Mobliz - Crescent Mountain Cave - Serpent Trench - Nikeah - Cave on the Veldt - Cultists' Tower
Kohlingen-Jidoor Region
Kohlingen - Jidoor - Zozo - Auction House - Opera House - Darill's Tomb - Mt. Zozo - Owzer's Mansion - Dragon's Neck Coliseum
Vector Region
Tzen - Albrook - Maranda - Vector - Magitek Research Facility - Imperial Observation Post - Cave to the Sealed Gate - Imperial Palace - Phoenix Cave - Kefka's Tower
Thamasa Region
Thamasa - Burning Home - Esper Caves - Ebot's Rock
Other Locations
Land of Espers - Floating Continent - Solitary Island - Triangle Island - Zone Eater's Belly - Dreamscape - Dragons' Den - Soul Shrine - Dinosaur Forest
Races
Human - Magi - Esper - Moogle - Yeti
Terms
Apocalypse - Blackjack - Eight Dragons - Falcon - Final Fantasy VI: The Interactive CG Game - Gestahlian Empire - Imperial Air Force - Light of Judgment - Magicite - Magitek - Magitek Armor - Magitek Knight - Returners - Warring Triad - War of the Magi
Music
Original Soundtrack - Grand Finale - Piano Collections - Kefka's Domain - Final Fantasy Finest Box - Final Fantasy VI Special Tracks - Final Fantasy VI Stars Vol.1 - Final Fantasy VI Stars Vol.2 "Battle Theme" - "Decisive Battle" - "Terra" - "Kefka" - "Kids Run Through the City" - "Aria di Mezzo Carattere" - "Relm's Theme" - "Searching for Friends" - "The Fierce Battle" - "Dancing Mad"
Doujinshi
Figaro no Kekkon: Tales from Desert
Abilities
Blitz - Bushido - Control - Dance - Desperation Attack - Lore - Magitek - Mimic - Mug - Pray - Rage - Runic - Shock - Sketch - Slots - Steal - Throw - Tools - Trance
Archives
Abilities - Armor - Enemies - Enemy Abilities - Bugs and Glitches - Items - Magic - Relics - Timeline - Translations - Walkthroughs - Weapons

v · e · dBugs and Glitches
Final Fantasy
Critical Hit Bug - Equipment Bugs - Intelligence Bug - Invisible Woman of Cornelia - Magic Bugs - Peninsula of Power - Running Glitch - Enemy Attack Bug
Final Fantasy II
Dual Wield Bug - Equipment Bugs - Magic Bugs - Middle Character Target Bug - Party Magic Target Bug - Peninsula of Power - Target-Cancel Bug
Final Fantasy III
Equipment Bugs - Item Duplication - Item Upgrade Glitch - Magic Bugs - Magic Duplication Glitch - Peninsula of Power - Walking Through Walls Glitch
Final Fantasy IV
ATB Glitch - Avenger Bugs - Equipment Bugs - Item Duplication - Lunar Whale Glitch - Peninsula of Power - Psycho Edward Bug - Reviving Enemies Glitch - Save Glitch - Sealed Cave Glitch - Second Form Glitch - Sneak Glitch - Sylph Glitch
Final Fantasy V
Airship and Hiryuu Glitch - Ancient Library Glitch - Berserker Class Glitch - Black Chocobo Glitch - Catch Bug - Encounter Glitch - Equipment Bugs - Faris in Tule Glitch - Hidden Zombies Bug - Hide Glitch - Infinite Items Glitch - Item Transformation Bug - Kiss of Blessing Bug - Mix and X-Magic Glitch - Optimize Glitch - Power Drink Bug - View Bug - Walking Through Walls Glitch - Walking in Air Glitch
Final Fantasy VI
0 HP Character Bug - Bypass Event Glitch - Capture Glitch - Desert Hare Glitch - Dream Stooges Bug - Duncan Bug - Empty Party Glitch - Encounter Glitch - Equipment Bugs - Evade Bug - Genji Glove Bug - Jump Glitch - Level Reset Glitch - Mantra Glitch - Master's Scroll Bug - Mimic Glitch - Opera House Glitch - Optimize Glitch - Overflow Glitch - Peninsula of Power - Pincer Attack Glitch - Psycho Cyan Bug - Rippler Bug - Save Point Glitch - Sketch Bug - Slot Bug - Snort Bug - Trance Glitch - Ultima Weapon and Petrify Glitch - Umaro Unequip Glitch - Vanish-Doom Bug - Walking Through Walls Glitch
Final Fantasy VII
Adamantaimai Cure Glitch - Aeris's Ghost and Sector 5 Church Glitches - Back Attack Glitch - Blackout World Glitch - Dancing Tifa Glitch - Diamond Weapon Glitch - Gelnika Rude AI Glitch - Going to Wutai Glitch - Infinite Elixir Glitch - Knights of the Round Glitch - Magic Defense Bug - Master Command and Support Materia Glitch - Midgar Zolom Save Glitch - Overflow Glitch - Pyramid Encounter Glitch - Quadra Magic Cave Glitch - Quadra Magic Ultima Glitch - Regen Bug - Reviving Enemies Glitch - Save Crystal Glitch - Save Point Glitch- Inescapable Battles Glitch - Vehicles Glitch - Vincent Mug Glitch - W-Item Duplication Bug
Final Fantasy VIII
Balamb Garden Balcony Glitch - Junction Glitch
Final Fantasy IX
Gold Chocobo Bug - Optimize Glitch - Thunder Slash Glitch
Final Fantasy X
Home Glitch
Final Fantasy X-2
Episode Complete Bug
Final Fantasy XII
Dead Character Glitch - Immobilize Glitch - Phoenix Down Glitch - Zone Out Glitch - Self-revival Glitch
Final Fantasy Tactics
Dragqueen - JP Scroll Glitch - Jump Glitch - Poach Bug - Quickening Glitch - Weapon Duplication Bug
Final Fantasy Tactics Advance
Shara Glitch
Final Fantasy Tactics A2: Grimoire of the Rift
Double KO Bug - Requiem Counter
Final Fantasy Mystic Quest
Overflow Glitch - Magic Bugs
Dissidia Final Fantasy
0 HP EX Burst Glitch - Ability Sort Bug - Chaos Intro Glitch - Double KO Bug - Holy Glitch - Invisibility Glitch - Jumping Capsule Top Glitch - Walking in Air Glitch - Chase Auto-Charge Glitch - Snooze and Lose Glitch
Dissidia 012 Final Fantasy
Holy Glitch - Double KO Bug - Walking in Air Glitch - Snooze and Lose Glitch