Want a few Visceroids to hide in a Tiberium patch to attack a passing infantry column? Or maybe a handful of Marauders to defend their Hovel? This tutorial will show you how to add hostile Creeps to your multiplayer maps.
1. Place your Creeps
You can use virtually any unit, as long as it can shoot. This also works for squads. Try to place them in strategic or natural places.

2. Add Skirmish Players
PlyrCreeps is what we're looking for here. By default, the team is already hostile to all players so there's no reason to mess around with any settings.

3. Team Up
Make sure all your Creeps are set to PlyrCreeps or they won't do anything regardless of the next settings.

4. Piss Them Off
Set the Stance of your Creeps to Aggressive. This will make them attack anything that comes into range. Also make them Targetable.

5. Test
At this point, your Creeps should stay in place and attack any unit that comes into their range, and disengage if they leave. Good sentries, but boring otherwise.

Now, getting them to move. . .