Cait Sith is a recruitable enemy from Final Fantasy XIII-2. When first encountered in the Bresha Ruins, they should be dealt first as they can quickly heal lost HP. Other than that, they are not a difficult enemy to defeat.
Cait Sith is one of the first two monsters tamed in the game, being part of a tutorial. Cait Sith is a Medic, and as it is unlikely Serah and Noel have access to the Medic role when Cait Sith is tamed, it is invaluable in the early stages of the game.
However, it quickly falls out of favor when the main characters earn the Medic role, as its stat growth is low until it reaches the last stages of its development. Once it does, however, it can prove to be a highly useful Medic monster for its sheer Magic power, which can be augmented to over 1300 with the correct infusions.
Its Feral Link, Kitty Clock, is weak, as it is based on Cait Sith's Strength stat, and only inflicts Poison if the target has zero resistance against the status. It is suggested only using the Feral Link when attempting to get a certain monster crystal with a low drop rate.