Someone please correct me if I'm wrong but, as with most mod maps, I don't think any boss areanas have been added to this map yet.

I looked into it and tried on singleplayer. You fall through the floor and die, even if you use cheats to fly you'll die after 60 seconds. This kinda sucks! I hope the dev kit gets fixed soon since I was really looking forward to bosses on my server.

I've had a similar problem to the floor death issue. I found a way around it by elevating yourself from the ground. I used cheat fly and hovered in the air, also building some structure to lift off the ground works too.