Pictures that focus on the animal-like characters and their bestial instincts. From a casual 'meow' to breaking out in a fit of rage. From what I had to study, there are three types of entries that make this pool work:

Type I - characters casually reveal their animal side.
Type II - characters use their characteristics for situational purposes (one example will be placed below).
Type III - characters "break out" their animal side, whether it is by intention, impulse, or rage.

There's likely to be some confusion regarding which entries are credible. These are a few exceptions. They may change over time.

I. No "full" transformations (i.e. animalizations ). The ideal of this pool is the artists' focus on the characters' emotions leading to their transformations. After all, animalizations are often used for simple, comedic, or symbolic reasons.
II. Vampires and Oni are a tricky case because they are capable of using their instincts naturally. What would make them credible is that they have to be Type III, acting by pure rage or blood impulses (there will be examples).
III. Much of the Youkai (those without animal-like characteristics) in Touhou's cast are rarely portrayed in any feral manner. Such pictures that do exist are usually Type III.