Trogs

Trogs is a purple cat encountered during the Swept Away quest, originally released as the 2008 Hallowe'en event. Trogs is Wendy's cat and players can talk to him with a catspeak amulet. Upon being asked about what it is like to be purple, he comments that he is getting used to it, although he is not sure Wendy has found a way to reverse the effect.

During the Hallowe'en event the player could talk to him to have a choice of 3 fixed conversations about Hallowe'en. Trogs would comment on your attire if you spoke to him. His comments varied depending on how many costume items you are wearing.

Two or more items - "Rather nice costume, that. Are you trick-or-treating this year, then?"
One item - "Oh, I see you're wearing one costume item! Aren't you planning on trick-or-treating this year?"
None - "No costume, eh? Aren't you planning on trick-or-treating this year?"

He would also tell you you can get something quick and easy by talking to the Fancy-dress shop owner in Varrock.

It is possible that 'Fraidy cat is an alternate-universe version of him.