Cityscape Fighting (Apocalypse)

There are two types of combats that can occur on Mega-Primus.

Aliens

Alien Retaliation

The aliens will target an organization and will conduct attacks with their craft with the propose of destroying the organization's buildings and craft. If the target is an X-COM Base then the entire structure can collapse (especially in the case of Slums). If the map square with the Agent figure is destroyed it will bring the death of any X-COM personnel allocated to that base.

Overspawn Attack

The aliens will drop an Overspawn into Mega-Primus with the objective of conducting massive damage to the city (and the corresponding negative impact on X-COM's score).

Alien Infiltration

The UFO's will hover over buildings and will either directly drop aliens into the building (through a transport beam visible on the Cityscape Screen) or try to directly subvert the organization (through the 'Micronoid Rain' attack which is also possible to see with Overhead View). If an X-COM Base is present at the building a Base Defense mission will immediately take place.

Alien Detection on Buildings

Usually happens as a result of the Alien Infiltration described above but sometimes there can be aliens detected in buildings, usually as a result of the aliens spreading out from buildings already contaminated by them.

Organizations

Raiding

Organizations hostile to one another will conduct economic raids which will be reported by messages on the Cityspace screen. X-COM can conduct raids of its own with the propose of recovering valuable items or as a means of punishment. If it is X-COM who finds itself targeted then a Base Defense mission will occur.

Organization Air Attack

Less frequently an organization might instead send illegal flyers to directly attack the buildings of their enemies. Sometimes it might be a good idea for X-COM craft to intercept and destroy illegal craft heading towards its allies or merely to prevent more damage inflicted to the city.