Sankaku Channel/

Difficult, especially with all of the posts where people don't realize it's an entirely different subject. The easiest example would be to find a picture with two Pokemon rutting it out, as they count as "animals".
The double-layered problem that extends further is that the majority of the questionable/explicit Pokemon pairing pictures are almost all of humanoid or human-shaped Pokemon, which drags the issue further into a grey area.They count as animals, but are anthropomorphic which throws both bars into question. (Part of the only real reasoning people are attracted to certain Pokemon in question.) An even greater deal of the same pictures are the Pokemon who are not innately humanoid forcibly made humanoid for the purpose of fulfilling the need for humanoid Pokemon to lust after.

An example of Zoophilia, and also Pokephilia, would be this picture:
https://chan.sankakucomplex.com/post/show/4067473

These Pokemon are opposites on the evolutionary scale, but are confirmed canonically to be able to breed in the same egg group, effectively bringing attention to the fetishists who share the same perversion. Please note that while Zangoose is bipedial, it is not a humanoid Pokemon, counted as mammalian (which further brings to question why it can breed successfully with a reptilian Pokemon.)
Now, there are more than enough examples of Bestiality in the Pokemon tag, but a excellent example would be this:
https://chan.sankakucomplex.com/post/show/4257935

I have no way to properly expound on this picture, as I feel it is self-explanatory: Drawn for the purpose of Dawn (Hikari) being fucked by a Rapidash. Bestiality, clear-cut.

The biggest difference between the first and second pictures are the presence of a human, a non-animal in that sense. Without the involvement of a human, the picture is not Beastiality but Zoophilia for it's intentions. However, a proper Zoophilia picture can have humans that are not involved in the actual process of the explicit portion of the work, such as Pokemon Breeders as long as they are not participating--but facilitation does not mark Bestiality any more than observation would. Essentially, Bestiality comes down to whether there is a human getting fucked/fucking/masturbating/etc. an involved non-human party. Nezunezu is a prime example all-around, particularly towards Bestiality and Pokephilia.

I suppose I should also clarify that Pokephilia is a broadened term for the Pokemon fetish in general, as opposed to being a situational tag as on other websites that I've had the untimely pleasure of frequenting. It's more commonly used to describe a single Pokemon in a perverse or explicit situation, such as a Gardevoir masturbating, etc.. This however does include Pokemon Pairings, such as the previous Zoophilia example provided as the emphasis is on the Pokemon portrayed, and their explicit situation as a combined focus.

...I apologize if my response is overly-drawn out, or perhaps too complicated. I also apologize if my tone sounds a deal more rigid than necessary.