The Men in Black
A secretive agency, originally part of the government but now apparently a private organization ("the government asks too many questions").
Representatives of this agency wear sunglasses and dark suits, and appear at UFO landing sites. The MiB use devices known as Neuralyzers to wipe their memories and suggest more mundane causes to the encounter (or anything else the agents think of). Neuralyzers are typically the size and shape of an oversized pen and can be set to erase memories as far back as several years. Neuralizers are also used on agents who leave the organization for any reason. The MiB's sunglasses protect them from the effects of the Neuralyzer.
The MiB's main aim seems to be to collect aliens specemins, both biological and technological, and back-engineer them in order to manufacture highly effective weapons and equipement.
Nobody is quite sure what they actually plan to do with this equipement though.

The MiBs work in pairs. Their main force is comprised of five teams of Operatives. Each operative is equipped with a variety of weapons and tools issued for the task in hand. They have the ability to upgrade their weapons with salvaged alien technology so you never know what you're going to be facing should you be unlucky enough to oppose them.

Occasionally the MiBs deploy a Clean Up Team, usually deployed in two sections of five men each. These teams often travel in trucks using Military or Government markings to avoid close examination by civilians. The job of the Clean Up Team is to secure an area from outside interference and recover larger pieces of alien technology.
Figures are all sculpted by Mark Copplestone and are available from Copplestone Castings and Em-4 Miniatures.
Vehicles are diecast from various manufacturers.

Alien Invasion Rules for the MIB
MiB usually operate in pairs; each pair is a group. They move 8 inches. They cannot link fire.
Each time a group shoots it rolls a D6 to see how many actual D6 to roll when it shoots, this score is for each operative in the group. MiB's firepower will be weak at the beginning until they know what they’re up against.
The first time an alien species is killed the MiB player gets the miniature to study. The MiB player doesn't need to get an operative next to the dead alien or anything, getting the miniature is automatic. Each action spent studying lets the MiB player roll 1D6 for each group on the table. A 6 is a success and adds 1D6 to each initial shooting roll. This success is only available once per different alien.
When fighting Spugs for instance there are three alien races, Spugs, Mites and Burrowers so three successes are possible during the game giving a total fire power of 4D6 x D6 (a possible 24D6) for shooting. Normally however, there will only be a single upgrade available, allowing a possible 2D6 x D6 shooting dice per operative.
MiB are protected by alien devices and require 3 more than what is normally needed to kill a human.
Open-9, Cover-12, Building- 15.
MiB Clean Up teams arrive with heavy weapons when a Special Action card is drawn.
Clean Up teams operate in two sections of five men comprising a leader, four troopers and a light support weapon. Each man rolls D6 equal to the current successes +1 for shooting. This is because they’ve been deployed from HQ equipped with the current ‘best intel’ weapons for the job. Therefore, if only one success has been made before they arrive each man will roll 2D6 per shot. The heavy weapons in each squad get an additional D6 to this. Clean Up sections can link fire and both sections get an action per action drawn. This means that one section can shoot and the other move as a single action, or both could shoot at the same or different targets etc.
Deployed Clean Up teams do not add to subsequent study rolls nor do they reap any benefit from them.
In addition to any scenario specific victory conditions, the MIB can claim a victory once they have made a success roll for every alien species present.