Bosses are going under the map, but also not going under the map. I don’t know if it’s specifically different for host/client or a random player or player/spectator. But I’ll explain it from my experience. In these instances the boss appears to be under the map, but behaves as if they aren’t.
Seeing is believing:
That by itself doesn’t make much sense and it seems as if the Rat Ogre burrowed under the map and popped out like a new type of Mole Rat Ogre.
Here, we see a nearly identical situation but this time the Chaos Spawn seems to grab me from underneath the map:
This is the same scene but from the perspective of the host/spectator.
So for the first Spawn video it looks as if I’m wondering what the hell it’s doing and am unsure as to what it’s going to do, before it pulls me under the map and then drops me into the abyss(My friend described it as the Balrog pulling me under with it). When I spectated my ally, the Spawn had popped out of the ground and was normal again. In the second Spawn video it looks like I just stood there and made no attempt to dodge it for some reason.
Now, despite those things being different, the one thing that remained the same is me dying instantly after nomming my hp to 0, rather than being placed on the ground in a downed state. This would seem to suggest some kind of desync going on. I believe there is an invisible wall or something by that thin catwalk I seemingly knocked the Spawn off of. In the Athel Yenlui one, I’m pretty sure the boss hit an invisible wall there too. My speculation is that the boss hits the invisible wall and desyncs, causing it to have at least two differently behaving instances of itself. It’s like being above the ground and below the ground at the same time, doing the same actions.
This is the same spot on Athel Yenlui. I’m host and can’t get the boss to drop or do the issue. When jumping, there seems to be no invisible wall but it’s actually just a little further out. This causes the big boss unit to be unable to drop off but allows players and smaller entities to fall off. You can see me hitting the wall mid-jump though towards the end of the video.
Slave rats can clearly be bumped off and the game chooses to delete them shortly after they land on an invisible floor. Sometimes the game fails to do this and the rats clip into the ground and can follow/attack players.