A sort of idea that I had for this. Since pets are important things in canon, it's often a thing that the pixel design shown for them isn't really accurate or is of a fairly abstract design. I thought that some of the notable canon pets could be given descriptive designs based off of their appearance as well as slightly off from it. A major theme going along with it is that a lot of the designs will be humanoid based due to it not being all too abstract and all. (I'm going to look for approval on all of these, of course, and I'm not going to try to force these designs on to everyone or anything like that, these are just suggestions that I think are cool enough to present to you guys.)
Ergoth's head is a white, rounded cap that appears slightly like a mushroom, which takes up the majority of his head. The other part of this is a white cylinder-like head shape. He also has large, red eyes, and a greyish muzzle in the area of his mouth. The head actually appears and acts similar to a helmet instead of his real head. He has a muscular, burly build, and is slightly taller than Rev. His body is brown like seen in his sprite, and he is visibly very muscular, as fitting with his great strength. He doesn't wear clothes, but he doesn't need to as his body does not contain those parts on his person, as those areas are merely smoothed out parts of his body. (More about this when I understand pet breeding, bluh.)
Trix basically looks like a girl that's her age (Whatever this is officially in the Trix stories). She has a mostly humanoid body, but with some clear differences. She wears clothes, apparently; a simple brown shirt, a rounded/circular skirt (Based off of the UFO part of her body; also she has the ability to float still and all), orange leggingsocks and red boots. Her skin is a fiery colour, and possibly changes if certain factors (emotions, powering up, etc.). She also has bright red eyes. She also has short hair of another fiery colour, which also has four split ponytails (lol pony), which are meant to reference the appearance of her head (Though the design makes them all appear diagonal).
Emotion is basically just like a 'Dark Matter' form (Regular Dark Matter forms, not in humanoid form), with yellow/brown robes, the only differences being that he doesn't have the face garments and instead just a somber expression, and also his 'hair' is style like the petals of a beautiful flower.
Veyron appears as an eel-like creature just below the size of a regular human. Her body, from head to tail, goes across the spectrum of the rainbow (only in slightly darker colours). Her head actually appears somewhat reminiscent of a human face, or possibly actually like a sea-dweller Alternian troll. Her eyes are lighter colours of the dark colours that circle around her form. She also has lighter spots similar to her eyes over the front of her body at certain intervals, giving the sort of appearance of having many eyes.
More ideas coming soon when I think of good ones...
General species notes
This whole thing will kind of stretch the whole species base thing, kind of making a lot of pets look mutated. I can give general design ideas for some species whenever I think of them...