Presence

Believe it or not, but Final Fantasy VII wasn't the first game we saw Cait Sith in—not only that, but he's made appearances in other games, as well.

FinalFantasyVI

In Final Fantasy VI (previously released as Final Fantasy III in North America, but having since been re-released under its original title), Cait Sith was first seen as an esper named "Stray", one of many creatures born of a long thought lost magic. During this time, Tetsuya Nomura, who was the character designer of FFVII, was an enemy designer of FFVI. Apparently, he liked Stray's design so much that he decided to re-use it when designing Cait Sith.

Stray is one of the four espers originally acquired in Zozo. Its main attack is "Cat Rain"; using 28 MP it attempts to confuse the enemy. Its Level Up Bonus is "Magic Power +1". Characters equipped with Stray can learn the following magic spells:

Name	MP	Learn Rate
Muddle	6	x7
Imp	22	x5
Float	3	x2

FinalFantasyX

Cait Sith later appeared in Final Fantasy X as a weapon. Cait Sith is not only mog-less, but has taken on the type of inanimate object that his previous mog companion subscribed to: a stuffed doll. Wielded by Lulu, the Black Mage character, Cait Sith is a small voodoo doll, about two hands tall, that has come to life at its master's command. Lulu generally uses Cait Sith and her other dolls as magic enhancing weapons that aid in the casting of spells; but Cait Sith and the other dolls are also perfectly capabale of running up to the enemy and attacking them physically, this not being highly recommended as Lulu's attack stats are extremely weak. However, by doing a physical attack, you can also hit the enemy with any status effects equipped to the doll, such as poison.

Cait Sith is dropped by both the fiends Garuda and Sinspawn. Cait Sith is Lulu's second strongest weapon in the game (next to the Onion Knight). It cannot be purchased, although you can sell it to O'Aka, the traveling (and quite poor) salesperson. Cait Sith, using Rikku's Customize ability, can be customised into various other versions:

Quiet Cait Sith (poisontouch)	Sleepy Cait Sith (sleeptouch)	Noxious Cait Sith (poisontouch)	Fossil Cait Sith (stonetouch)
Late Cait Sith (slowtouch)	Fatal Cait Sith (deathtouch)	Dark Cait Sith (dark strike)	Mute Cait Sith (silence strike)
Dreamy Cait Sith (sleep strike)	Toxic Cait Sith (poison strike)	Stone Cait Sith (stone strike)	Chronos Cait Sith (slow strike)
Wicked Cait Sith (death strike)

Or, you can use combinations of items to create weapons:

Ominous Cait Sith (2 or more of the "...touch"es)	Abaddon Cait Sith (3 of the "...strike"s)
Chaotic (4 or more of the "...strike"s)

Source: Weapon details from FFOnline

FinalFantasyX-2

Cait Sith's most recent appearance is in Final Fantasy X-2 as the Mascot Dressphere for Rikku (FFVIII players may also recognise PuPu the alien as the creature Cait Sith is holding). Dresspheres are just as they sound: spheres that, when equipped, become a dressup changes not only the physical outfit of the character, but also her stats and abilities.

MASCOT (Cait Sith)
Acquired from Brother after you get an Episode Complete! in every area of Spira
Special Abilities
Attack	Damage to one enemy
Cait Fire	Fire damage (occasionally Poison/Petrify)
Cait Fire	Thunder damage (occasionally Poison/Petrify)
Cait Fire	Blizzard damage (occasionally Poison/Petrify)
Cait Fire	Water damage (occasionally Poison/Petrify)
Power Eraser	Lowers all enemies' Strength
Armor Eraser	Lowers all enemies' Defense
Magic Eraser	Lowers all enemies' Magic
Mental Eraser	Lowers all enemies' Magic Def.
Speed Eraser	Lowers all enemies' Evasion
PuPu Platter	Sometimes instantly kills all enemies
Ribbon	Immune to status effects
Auto-Shell	Automatically casts Shell
Auto-Protect	Automatically casts Protect
Instinct	Use Berserker dressphere skills
White Magic	Use White Mage dressphere skills