Yilly Katt is a humanoid with an elongated, oddly-bony, head and a very unusual ability: like many animals in the world of nature, he is capable of changing the colour of his skin, although unlike these creatures, Yilly can do so at will, displaying an astonishing variety of hues, from the bluest of skies, to the most golden of corn, to the fieriest of sunsets. He will often use this talent to remind that element of Midian's population who miss the sun's warm touch of what it was once like to experience the kiss of daylight, bringing a small measure of happiness to those wretched beings.
Yilly's skills with his bodily pigmentation are not merely limited to recreating the shades of the sky, however, and at times (particularly when under the influence of substances provided by the Thrall) he will lose control of his genetic gift and manifest an unbelievable depiction of colours, hides, scales and patterns in speedy succession across his entire form, appearing, as one particularly cynical commentator noted, "Like the Breed remade in one body; everything and nothing; mess and pain and flesh gone mad." After these episodes, Yilly claims without fail to have seen God, to which some wit typically responds with: "But did He see you? Did He Hell." Who can be sure, though? Maybe He did . . .
What happened to Yilly after the Sons of the Free attacked and destroyed Midian is unknown.