Does a custom overlay have to be true to the pet's species and color? This is what I am used to on other pet sites I have been on; however, there does not seem to be anything in the rules (that I've read) that prohibit us from drawing anything we want.

Personally I want to upload a design for a character that does not look like any of the default pets here on Subeta (yes, I've considered Experiment pets as well). The Zasaba comes the closest.

If a total replacement wasn't possible is there a possibility of me getting away with drawing something close to/reminiscent of Zasaba? Has that been done before? I wish I had a reference of my design but I don't have one finished yet.

These are the official rules for custom overlays:

Keep it PG-13 and well within the current Subeta rules. No stealing artwork that wasn't made for or purchased by you. Quads and anthros only please - no humans, kemonomimi/gijinka, or inanimate objects. Fullbody artwork only - no busts/headshots. No images that represent pets from other pet sites. Props are allowed, but no minions or extra characters. No unaltered official Subeta artwork. Each image must be unique - two users cannot upload the same overlay.

So yeah, it doesn't really have to be exactly like one of the existing pets if you want to do something kind of different. Most people will pick a pet species and color that is similar to what the overlay will be like. I'm pretty sure you just aren't allowed to mislead people into thinking you have a certain pet that you don't, so like your pet's profile should still have the name and "Custom ___ species" underneath it (so like, don't try to pretend you have an Angelic Lain if it's really a common Ruffie or something like that).

[edit]Link to the other rule about no misrepresentation: https://subeta.net/help/rules.php?act=rule&id=59

Thanks for the input! So if I understand correctly, so long as we are not trying to impersonate another species+color already existing on the site it should be okay?

That's how I understand it as well! And I've seen some overlays that are meant to represent characters from like TV shows and stuff, and while they weren't human because of that rule the overlay wasn't necessarily like one of the existing pets either. So as long as you follow those rules and aren't trying to lie about what kind of pet you have, it should be okay!