i *think* the only UCs that really need a guide are the mid/high UCs. everyone knows that the lower tier pets trade badly, and everyone ALSO knows that the rare UCs can trade for literally anything
so really we only need a "tier" for figuring out if trading a VWN UC Faerie Xweetok is a "fair trade" for a VWN UC Plushie Blumaroo
Faerie Techos and Darigan Wockies should both be in the rare tier and i have no idea why they arent.