The lower part of the middle tube, where all the powerups are, is an excellent chance to get some free frags or just lower your foes frag counts.
Knockback weapons are very useful in this map, especially if there're some people near the ledges of a level.
Actually the mapper placed the invisibility of Unreal which UT replaces with its own.
I just wanted to do something weird and brutal, where fight is the only goal of the Level, and where gathering Items is secondary. The Tube in the middle allow you to fly from floor to floor. The Level is oversimplified but the resulting gameplay is interesting. You can go under the basement level to get all the goodies but it's risky since anyone who sees you can send you flying in the sky.