"Marker" you see everywhere no matter how far you are

Hi ! I am trying to make either a Mob or a Structure or some kind of vanilla particle to display no matter how far you are. (It is supposed to be a big skull floating on top of the dungeon to "mark" its opening.) I really don't think it is possible and even less possible with the 1.12.2-forge generator. I am on the latest 2020.5 version.

Thanks for any feedback, even if it is confirming my thought. (I tried with a 3D model of a mob with viewDistance at like 10'000 or 1'000 , don't remember but it sadly still "despawn" from view at the end of my Render Distance.)

Also, the only reason i'm still on 1.12.2 for THIS specific mod, is that it's on a "given map" i made, and it needs some mods that will probably never update to 1.15.2. (Like Davincis Vessel , which is crucial for this "gamemode")

Feel free to ask for clarifications.