So, slugcats presumably dont need to have intercourse to have pups. So they can as*xually reproduce babies of TOTALLY differing color. How does this even happen sisters-

The age old question, is it any similar anatomically to a slug OR a cat? Some may think it's slimy but I contest by saying if you get large enough, you'll have a hard time passing through small, tight spaces. Unless of course, if you smash some fruit on you to make you slimy and MOIST, letting you pass through easier. Also it would be hard to grip and throw objects if your hands were wet and slimy, slipping things out your hand. Not the mention the fact that if you pay attention, the scug, in tight spaces will CRAWL through similar to an animal like a cat. This is similar to how other species, like lizards or scavengers will walk relatively similar. With also knowing that they too, are not slimy. Also we can kinda confirm they're fluffy from the fact that saint has visible fur. And it's ♥♥♥♥♥♥♥ pixel art, they cant be that fluffy normally.

Well, that question cant really be answered. If we're going off real life, it's more of a cat then a slug, the only features that make it slug are it's size, and it's tail. But regarding the as*xual reproduction thing, some species of slug can reproduce as*xually. The best example is the Deroceras laeve, differing in colors similar to the scugs' patterns.

Rivulet is probably just a "Seascug" (Slugcat + seaslug)

Spearmaster doesn't have a mouth, and kind of acts like a mosquito. Stabbing you with it's little needle, or I guess it's proboscis, it sucks the blood out of a creature. So it would be a moscug, mosquito slugcat.