The setting can easily be changed to Earth (1950s onward); the Brain could also be a mutant created by atomic tests, a humanoid alien with oversized head, a colonist mutated by exposure to radioactive ore, etc. I just happened to have made a giant flying Brain using DAS. For that matter, it should be easy to adapt this for other sets of rules.
Location:
The backwater world of Kole Minor. A small colony is located here, consisting of a town with Class D starport and some outlying mining settlements. Some of the inhabitants are human, but a few are aliens.
Situation:
A strange light was seen in the sky several days ago, possibly a ship. The colony has no real sensors (nor does the starport), but a search was made by aircar. This turned up nothing, so it was presumed to be some sort of atmospheric disturbance ... until several of the locals began acting strangely!
A growing number of colonists began acting secretive and ignoring activities that were previously important to them. Investigation by a Imperial lawman (IISP Officer Kowalski, who had stopped off on the colony to make some minor repairs to his one-man scout) revealed that the colonists had been mind-controlled by a hideous, giant alien brain!
Officer Kowalski and the unaffected townsfolk retreated to the spaceport building, but found that the Hyperwave had been destroyed by a controlled technician. A scientist managed to cobble together some Encephalo-Static devices, which would render the wearers immune to the mind control (though not the thing's brain bolts). With this protection, Officer Kowalski and some armed colonists now return to destroy the Brain.
Setup:
A small town. In the center of the board is a largish building where the Brain lurks (a warehouse in our game). Next door is a taller building (Martian Joe's). Other buildings, parked vehicles, etc fill the board.
On the roof of Martian Joe's is a sinister device that will boost the Brain's mental powers, letting it control everyone in the area (even those wearing ESDs). A small robot is currently working on the thing; when complete the Brain can tap into its power from anywhere on the board. The device will be complete when 10 face cards have been turned for initiative. The robot cannot be seen from the ground (Arland Monowheels are very short!) and the weaponry carried by the colonists cannot hurt the device - unless someone can get onto the roof and smash it from up close. Being subject to the Laws of Robotics, the robot will not attack sentient beings. It will, however, make agitated beeping noises if someone chucks it off the roof or the device is smashed.
Forces:
The Brain: REP 4; ignores low obstacles because it floats a few feet off the ground. Can fire Brain Bolts (Impact 2) to anything it has LOS on; these ignore cover, movement, etc. If the Brain dies, all its minions are freed from control.
The Brain has a number of colonists serving it. These are rolled up in Chain Reaction as Civilians (but everyone has at least a pistol).
Officer Kowalski: REP 5; armed with a pistol.
The uncontrolled colonists are generated the same as the controlled ones (but see note below).
Controlled colonists start the game hidden. The attackers choose which edge to enter from.
We had 10 colonists per side, plus the leaders. In retrospect, it might have been better to increase either the number of attackers or their REPs. In the latter case, treat rolls of REP 2 as REP 3 for the uncontrolled guys (the controlled ones are subconsciously fighting the Brain's power and therefore not acting as effectively).