|Final Fantasy X-2 Boss|
- Normal: "A serpentine fiend that shoots a strange beam from its eye. Though it primarily uses physical attacks, its Stony Glare and Heaven's Cataract will give you the most trouble."
Oversoul: "A fiend that can turn objects to stone with a glance. It petrifies its prey with Stony Glare, then prevents them from recovering by destroying their Softs."
Chac is a very difficult enemy. She can petrify characters with her Stony Glare attack, which works regardless of immunities, but can be evaded with high Evasion and Luck stats. Chac never uses Stony Glare if only one character is present. Chac can break a petrified character with her Bash attack, removing them from battle.
As with all Basilisks, Chac does not use Heaven's Cataract in Oversoul form, and many consider Chac to be easier in Oversoul. The Oversoul attack pattern includes four additional attack types: Destroy Soft and Destroy Remedy, that also do damage, and are used unless an Alchemist is in the party; Bash replaces them. She can use MP Break to drain all of a character's MP, and on characters at half health or below, an attack that does no damage, Hunter's Gaze, is sometimes used. The net effect is a significant reduction in overall damage and even risk of KO.
In the International and HD Remaster versions, the easiest way to deal with Chac is to drain her MP. If she has no MP, she cannot use her dangerous Heaven's Cataract move, and is thus helpless against a team of Berserkers with Evade & Counter. Draining her MP can be done in various ways, the easiest of which is by using a Soul Spring. Heaven's Cataract will not cost MP in the original version, and this strategy will therefore fail.
In the original version, an uncomplicated and effective way to defeat Chac involves bringing a Gunner in HP Critical condition that is wearing the Cat Nip accessory. Using her Trigger Happy ability will result in 9,999 damage per hit. Against an Oversouled Chac, the third-HP character will not be hit by Heaven's Cataract, and roughly 14% of the attacks will be replaced by the harmless Hunter's Gaze.
Equipping the Adamantite accessory to either a character wearing the Berserker or the Dark Knight dressphere can help survive the powerful attacks Chac uses; a downside is that the attack rate will be lower than usual.
Another strategy is to use three hasted Warriors using Delay Buster (again, only works on an Oversouled Chac), denying her from ever getting a turn. Chaining attacks on Chac also delays her turn; three fast Thieves, especially hasted (with Speed Bracers), can defeat her without her getting a chance to attack as Thieves attack twice per Attack command, and if they attack one after another they build a continuous chain. This strategy can be used to unlock the trophy Full Chain in the HD Remaster version. The player can set ATB mode to Active, ATB speed to fast, and have First Strike either from Thief's auto-ability, or the Highroad Winds/Mounted Assault Garment Grids. Yuna and Rikku can equip Strength boosting accessories. For a specific strategy Yuna and Rikku can forgo Haste-giving accessories, while Paine equips Bloodlust and Wring, then replace Paine's accessories with Cat Nip and Haste Bangle/Speed Bracer. In the battle the player can try to time Yuna's and Rikku's normal attacks with Paine's to create a chain, with Paine as main damage dealer for her fast attack animation with Haste providing least time loss while maintaining chain; Yuna's and Rikku's longer normal attack animations at normal speed keep Chac in stagger longer.
An easy way to defeat a normal and an Oversoul versions of Chac is to bribe her with 1,751,400 gil in normal form, and 1,838,972 if she's in Oversoul, through the use of Lady Luck dressphere, or use the alternative way of bribing by using Slots without spending gil.
As Chac never uses Stony Glare if only one character is present, one can consider fighting Chac with a single character. Chac's non-Oversoul version's physical attacks can be dodged with the Berserker dressphere's Evade and Counter ability, making her Heaven's Cataract, which she uses at any whim, the sole move a single Berserker will have to fear.
In the Fiend Tale endings, another notable Chac was created from the spirit of a sailor's son who was among many who were killed by Sin, his village destroyed. Regardless, Chac ends up gaining a new family in fiends and teaching his adopted son what he learned from his father.