Viral Chao are special Chao intended to be released at official events for Sonic Chronicles: The Dark Brotherhood. The five Chao were named Stugs, Pooki, Fimbley, Baki and Farfinkle, and were intended to be obtainable to the public via special events. However, only one of the events was held and the others were cancelled, most likely down to poor attendance sales. Therefore, only one of the Viral Chao, Stugs, was officially distributed, making the other four Chao inaccessible without use of game-altering devices. The Japanese release of Sonic Chronicles: The Dark Brotherhood, which was released later, contained hidden codes that can be used in the Chao Garden to unlock four of the Viral Chao; Pooki, Fimbley, Baki and Stugs. These codes were later made available on the Japanese website for Sonic Chronicles: The Dark Brotherhood.
All Viral Chao have the same basic appearance; a black body, a rounded head and a black head-orb. Each Chao also has a colored strip on their heads covering their eyes, resembling an eye mask, making each Chao somewhat resemble a ninja. These "face masks" are colored differently depending on the Chao: Stugs' is white, Baki's is pink, Fimbley's is blue, Pooki's is red and Farfinkle's would have been orange.
Stugs: Bonded character is avoided by enemy attacks except when the character is the last surviving target.
Baki: Bonded character making a successful counter move will automatically get free attacks against the enemy. Additionally, the character's Damage stat is increased by two.
Fimbley: Bonded character will automatically be missed by some basic attacks by up to three basic attacks/rounds.
Pooki: Bonded character's Armor stat is increased by six and spreads the remaining damage evenly among other team members.
Farfinkle: Bonded character automatically inflicts a random status effect on enemy when making a normal attack. Additionally, the character's Damage stat is increased by two.
Farfinkle was not included in the list of unlockable Viral Chao in the Japanese release because it has a severe glitch causing 'KO' to be a status effect. If this happens, the affected enemy may try a POW move but cannot, forcing the player to shut their Nintendo DS down. This is the only Chao not released to the public.
The Japanese cheat code to unlock Pooki is BABYBABY.