The Bestiary now shows a general Stream appearance rate for all Stream creatures on each Stream creature's individual Bestiary page. The categories in order from most frequent to least frequent Stream appearance goes thus: very common -> common -> uncommon -> rare.
Do note that creatures that show in the same category might still have somewhat different appearance rates within their category.
For our current 158 Stream creatures the division goes like this:
Very common: 44 creatures
Common: 64 creatures
Uncommon: 30 creatures
Rare: 19 creatures
No category: Lakiran Platypus, due to their floody nature.