Well, its apparently the worm from dune. I found it in theater under the map, The Rig. Its under the strangely different and familiar rig in the distance.
Its a pretty cool Easter Egg that I believe no one else found yet. I searched and got no results, so I believe I’m the first to find it. EDIT: No, I’m not, but now I know how to activate it thanks to helpful people. 
https://account.xbox.com/en-us/gameclip/5aa87eaf-2001-418c-abdc-28a65b41c9ee?gamerTag=TGC%20Brony%20TO&scid=1370999b-fca2-4c53-8ec5-73493bcb67e5
Edit: Sorry the link didn’t turn out properly. I’m posting from a phone and it isn’t cooperating.
Edit 2: Turns out, you ground pound the circular object in the middle of the map then shoot some cores that pop up on the edge of the map to see the worm eat the distant rig. :3
you activate it by ground pounding the middle circle thing at the open pit and then going to the side and shooting the cores that come up
its the worm from dune
> 2535436901034715;2:
> you activate it by ground pounding the middle circle thing at the open pit and then going to the side and shooting the cores that come up
> its the worm from dune
Thanks for the info. Op edited and now I’m even happier with this Easter Egg. :3
That’s a great Easter egg 
Multiplayer competitors will not fear
Fear is the mind-killer
Fear is the little-death that brings total obliteration