This film shows a Marathon 2 demo game I played in the Thunderdome level in which I placed both BOBs and aliens with the demo object placement editor (DOPE). Check it out -- it shows how much fun you can have if you just modify the M2 demo Map file a bit.
To view the film, or to play a game yourself using the same conditions I used, you must
use DOPE to modify the Thunderdome level. Put in two of each BOB (green, blue, and brown), with a min and max of two each; one 3x recharger, with a min and max of one; one minor compiler, with a min of one and a max of two; four major fighters, with a min of four and a max of twelve; two rolling grenade-tosser/flamethrowers, with a min of two and a max of six. Give each a random placement, with maximal extras and replenishment. DOPE can be found at amug.org/incoming, I think.
To play the game, play level four (hold down the command and option keys when clicking on "New Game") on Total Carnage. And remember to find that 3x recharger whenever your health gets low.
Of course, you should modify and use a COPY of the demo Map file.