WHAT is an "Oil Dog"

had this question for a bit but just now thought to ask it on here - what is oil dog and why do I keep seeing is occasionally pop up

I think the first instance of me finding it was on the new Homestuck store (the shirt and stickers) and I was just like "Is this some kinda new joke I missed out on ??"

then at the end of the hit song "a home's stuck" there's this spooky ominous creature at the end which I THINK mentions oil Dog at some point it's really hard to understand
so yeah just wondering if anyone could explain what oil dog is lmao