[Molly]

Events like this don't need to be hard coded, they can be scripted really easily, either by making the script load a sufficient number of aggressive and roaming mobs directly, or by making a closed room where the mobs will load, and then start the invasion by just opening an exit from it, so the mobs can pour into the city. A few warning echoes to make it look good can also be handled by the script.

You can either make the script start the invasion automatically at given times, or start it manually, by some imm pushing a button, when they feel the time is ripe for an invasion.