None, just his own innate telepathic and empathic powers.
Who would suspect a pet cat as the instigator of a world in chaos? He appears to be a fluffy white cat, regal beasts, the kind noble women keep around the castle as pets. Yes, they are mousers, but they remember their place in the Second Kingdom as Gods. Thus they are the pet of the puppet or the castle/ keep/ household mouser.
This cat form is material. It will regenerate from any wound eventually.
His real form? He is a red glowing ball of light, seldom visible except to those with astreal vision and mystic senses. He feeds of the pain, anger, and confusion of Humans.
His kind have been visiting the world since Beings have first had thoughts. They have taken many guises to facilitate their feeding. They have even been invited. The Second Kingdom summoned them to the world (defining their form), feeding them in exchange power.
Gathrack is one of the few still here from the time of the Second Kingdom. The others have been banished back to their realm (only a fraction resummoned). Gathrack is following his own agenda to create a proper feeding environment for himself and his kin. If the world achieves enough chaos, the banishing wards will fall and his kind will be able to return and feed.
Gathrack, like all his parasitic kin, never do the dirty work themselves. They let Humans do it. Once properly motivated, they are much more efficient at sowing violence and chaos than Gathrack’s own. (A fact which amazes them greatly). So over the millennium or so, he has been the secret instigator of various assasination plots, minor and major wars, and much marital jelousy and violent in the Noble and Royal houses of the world.
Oh, unless being touched by a priest, Gathrack is undetectable except as a miasmus of Evil (normally explained by the presence of the Evil Doer i.e. the Puppet).
This is a great character to explain sudden changes in people’s personality.
Oh. Nobody ever calls the cat Gathrack. It is normally Fluffy, Snowball, Mouser, or even Cat. After all Names are such a Human thing.
Unless the campaign is using cut scenes or a villians game, the players will probably never see Gathrack. If one does see the villian, he might be see the cat being petted, fed, or it might be sleeping in a window. The cat is just another window dressing. (It is also a nice contrast to see the Evil Villian who would bring untold suffering upon people dotting upon his cat.)
GMs: Never draw notice to the Cat. The Cat will also run away long before things get “sticky”. He has been around long enough to know when it is soon to be over (Damm those Heroes). After all a failed plan will generate lots of chaos to tide him over until his next meal.