Harping On About Harpies: Lazuli. Not evil unlike most versions of harpies (a given with the extreme Sugar Bowl nature of the site), but described as "almost as frightening as she is beautiful" nonetheless.
Human "Creatures": Adamant, Fortuna and Gemini are visually indistinguishable from humans (apart from Gemini's green hair.)
Leprechaun: Clover, one of the seasonal pets for the month of March.
Revenue Enhancing Devices: A growing number of creatures are only available through donation. Bribing Your Way to Victory is avoided: they don't count for achievements, so that people who can't or won't buy one aren't stuck with unfillable lines on the achievements page, and people who do buy them don't get an advantage in unlocking things. Also, missions never require donation pets to access, so donation pets are basically an extra feature with almost no effect on the rest of the site (except that you get a max energy boost for fully evolving them just like every other creature.)
You can also get exotic credits by buying them with the in-game currency of Uni Creatures's complementary game, UniFaction. Or you could pray that a ninja comes one day and gives you some. Someone still has to buy the credits to give them to you, though.
Sugar Bowl: The sugariest. This may be the result of a Lighter and Softer transition performed early in the website's run; before that, for example, the Arena featured teams of pets fighting instead of sports games (the description for the Moxie Potion still refers to "combat energy",) and the Nagi and Twap families were carnivores.