Wow. That's beautiful. I don't recognize it as either Master or Akro. Not a combo I am familiar with. Sorry I'm not helpful today. P.s. welcome to the forum!
If that is a slag, then Akro. Not Pelt or MFC.
However, it's one of those that if I stare at it too long, I can't tell if it's slag or a West Virginia swirl. So I'm going to stop staring now.
I seem to recall that I had a Jim Davis marble with an animal inside ... when I first started collecting .... do I have that right? .... did he make those? .... and I sold it.
Wish I hadn't done that!