I was wondering when this thread would get made, we had some decent ideas last night.
As this guy said, this race should be an actual solid player race, not "lol fetish". We pulled it off with Lamias, we can do it with slimekin.
Statwise, I think they would have at least a bonus to constitution, and penalty to charisma, as they're well... oozes.
Don't think they should be able to turn fully to liquid to fit under doors... seems too powerful, and not all oozes are pure liquidy, most have some sort of shape-ish, or just can't squish that much.