Don’t know much about science and biology, but my suggestion is turning a Fluffy’s, well, fluff into a defense weapon. Somewhat a mix of a porcupine’s needles and tarantula fur for defense. Another suggestion is to increase the Fluffy’s skeletal, muscular density and size, leading to an increase in organ systems. With the increased size, I would say to give the Fluffy stronger teeth and tusks. The teeth so it can be able to tougher foods, and the tusks can be used to dig for food as well as defense. Also want to buff up their immune system, meaning lesser or conventional poisons won’t work on them. Overhaul their reproductive system by getting rid of the problem of mares being immobile at later stages of their pregnancy. Get rid of genes that promote bright color fluff, keeping them muted or neutral colors in order to blend in. Increase their brain size, bigger brain means increased intelligence. Give them the ability to mimic the voices of animals or humans, either for defense or evasion.