Not sure if this needs a bestiality tag too.

Kikimaru said:

Not sure if this needs a bestiality tag too.

In Danbooru it's 'tag what you see' so unless you have a shot of the other fucker's shape, be it shadow outline or the penis is not human-ish you can't exactly put that. Unless in the source, like twitter or pixiv tag the artist him/herself put that tag.

Rathurue said:

In Danbooru it's 'tag what you see' so unless you have a shot of the other fucker's shape, be it shadow outline or the penis is not human-ish you can't exactly put that. Unless in the source, like twitter or pixiv tag the artist him/herself put that tag.

looks like it could be mewtwo's