The artists make their backgrounds I think... But if you mean the template (behind where they put the stats, name, ability, etc, I am guessing they have a template they can recolor to fit with their animal, then they add the stats, I dont think they have them for download tho...
Personally I use the free online program called sketch.io But it needs some getting-used-to before you can use it effectively. You also should allow it to save to your cookies, so you can have it autosave, and make multiple files you can come back to later and edit.
If you mean making it symmetrical, I will make half the animal (with any mess behind the gray outside of your canvas on sketch.io) then save the half, and take the half, copy it, flip it (make sure you using the saved IMAGE, not the edit-able file), then make sure they are both the same size, and put them next to eachother, save, and voilà!
Hope this helps! (ask me any questions, sorry if it was confusing...)
here:
https://imgbb.com/ >> Start Uploading >> Upload >> Open image in a new tab (double click/use two fingers same time) >> send url (copy and paste it)
Set the background as transparent. When making something, use a color extractor, google up the animal you're making, and drag the image there so the extractor tells you the precise colors. Also, Google drawings had guide bars that help you achieve symmetry, use them. There's also this thing called curve tool, which helps you make fins and stuff.
I used rounded squares and crescents for my leatherback skin. Use this for the colors.
The majority of the tail when straight is a fully rounded rectangle, and the tip of it is a heart. The tail then flexes out, and changes to rings at different lengths.
I then compiled the different frames of the gif together with https://ezgif.com/ , which then resulted in the finished art.
the picture is in the link I made it in scratch here: https://scratch.mit.edu/projects/168786954/#player clown fish ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ clownfish stats: speed: 70% health multiplier: 10.0 damage multiplier: 4.0 damage block: 40% armor penetration: 70% boosts: 1 oxygen time: 15 seconds temperature: 10 seconds pressure time: 5 seconds abilities: gives back half the damage you receive ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ also maybe you could add sea anemones and only clown fish could go into it and no other animal if an animal does they will lose health and I can draw the anemones just a suggestion