Brenjone and I had found the Marlix. I was told to kill it and bren left me As I was fighting it over the ocean I managed to get get a shot to hit it It fled into a nearby jungle and I haven't found it yet despite my searching.. Wouldn't a boss mob try to pursue it's opponent so it can kill me or did it even despawn? I don't know, I would like the chance to keep fighting it though.
They are set to be riding invisible invincible bats. Marlix is not in control of the bat so it just flies around as a normal Minecraft bat would but with Marlix on his back.
The enraged mobs seemed to have disappeared too along with it. That's weird because I wasn't even pvp logging during the fight
Brenjone had been leaving and coming back for a week and would always see him Edit: and right now was my own first encounter with that one