User blog comment:Lunasaur/Uncommon rare pets?/@comment-38699071-20190601025848

So,

Pets are "Uncommon" (Pets are only uncommon if they're a Promo Pet) when their features are hard to come by. An example is the Pet Ladybug: Most of the time you'll see Red ones with round spots, but some are brown with stripes which makes it uncommon since not very people make Ladybugs like that. Their worth depends on how uncommon the features are, usally being able to get up to 2-3 Black Longs more (for Big Promo pets, i.e. Seals, Maybe a Red Long for smaller Promo pets) depending on wether you're trading a collector or not.

Hope this helps!

~ Snuffles888