What, do you mean you want to know how to make flipped art? That's easy-peasy, I can explain:
The easiest and way to make good quality flipped art is with a transparent background already on the pet or pets you want to use. Some people don't use transparent backgrounds or don't have an image program that can handle transparent images, and their art often looks choppy because they've had to cut around the pet and whatnot.
In order to get a transparent background with your pet, you need to copy the pet's code and paste it into the forum. You don't need to make an actual post, though; I usually open a
new thread page and just click preview after pasting the pet's code. It'll show the pet and you can save the transparent image without posting. It is also a good idea to place a random item far below your pet so you can crop the image and still get your pet's feet.
Here is my example, Misha:
I just added an item under her, then copied+pasted her code onto the post, and now I can save it to my computer.
Now the work begins. I don't know what image editing program you use, but I use Gimp. Any program that can use transparent pixels is fine, such as Photoshop, Sai, or firealpaca. So, you need to open your pet's image in your art program, then you can do whatever you want to it; crop out the item and bottom bar, flip it, resize it, put two pets together, etc.
Hope that answers your question. If you need any more help, I'm happy to oblige.