Alien Buildings And Combat Tactics

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Overgrown fungus buildings... but no fun once inside!

Alien Dimension Buildings

The aliens have ten strange structures which seem to be of an organic design. They are all invunerable to damage.

A building's mission objective can be completed only once since it will self-destruct at successful completion.

The only way to destroy the organic structures is by ground assault with a large and heavily armed X-Com strike team. Attacking the fungus growths with craft weapons does not achieve anything.
Each oversized fungus must be researched to understand its purpose and importance. To start the building assault once landed at a building, select "Investigate Building" or "Raid Building". Both buttons do the same thing.
Do not move agents from a landed craft into the building. Keep them within the craft when you start the mission.
A brief is prepared outlining the mission objective so that each building can be disabled.
Once an objective has been completed a message: "Building has been disabled" appears. The mission completes if no more hostiles are present. X-Com troops can hunt down the last remaining aliens or escape via available blue-exit-tiles to force an end. There is no rush to escape! The alien building remains structurally sound once it is disabled.
When returning to the alien 'cityscape', the building automatically starts to collapse. Do not launch your craft immediately since they may be damaged from the still self-destructing building. Return to Mega-Primus at your leisure!

The Sequence

One building chamber can only be attacked at any time. Once one growth is destroyed, a new research topic becomes available back in Mega-Primus.
1. Sleeping Chamber
2. Food Chamber
3. Alien Farm
4. Maintenance Factory
5. Incubator Chamber
6. Control Chamber
7. Spawning Chamber
8. Organic Factory
9. Megapod Chamber
10. Dimension Gate Generator

Internal Features


  • Ramps are very common and are used by ground units. Strategic removal of some ramps can easily funnel hostiles into an ambush.
  • Walls are fibrous and are resistant to damage. Each generic wall cell must be damaged up to three times (fibrous, stringy, rubble) before collapse is possible.
  • Stone embedded wall cells of any type do not have partial destructions. If it is damaged enough, it disappears. This can help if needing to tunneling through a wall quickly.
  • Curved edges (the bull-nose shape) of elevated sections cannot be walked on. They are weak and must be destroyed if wanting to jump off with your agent.
  • Stringy-type vertical plants are usually clustered together. They are weak and flammable but can hide a unit.
  • Platform sections with intergrated grav-lift can use the lift as structural support if all foundation parts are removed. Grand collapse may be possible if adjacent cells are destroyed. Caution with falling debris.

Exotic Plants
Alien plants (shown here) which have a reaction to destruction but are not mission objectives. Other biological growths do not have any battlescape effect. Area-of-effect is typically a radius of two except the large yellow-bright barrel with Stun Gas effect having a radius of nine. Not all are pictured: Acorns (pedestal and overhanging), Rotten Egg, Pink Pods.

Re-Inforcement Pads
These square-shaped devices found within every alien building are used to spawn-in more aliens.
Every alien building will have multiple spawn pads usually clustered with smoke and explosive plants. A common brown rock-type structural overhead scaffold is typical and easily indentified. Destruction of the spawn pad is possible with strong explosives. Each pad will destroy the immediate area with a small (3x3) explosion for each quarter of the complete pad. ie: each individual pad will have four explosions before disappearing.
Green pads only appear in the final building.
The small picture shown in overhead view is the same for both colour types. Some pads may appear mismatched in overhead view. This is a visual artifact and does not affect the pad's operation.
Blue Exit Tiles
These battlescape tiles are usually invunerable whereas some found within alien buildings may not be. A strong explosive may destroy them.

Alien Re-Inforcements

Aliens present within other structures are able to travel via their 'people tube' network. Any building which comes under attack by an X-Com ground force will prompt the alien horde into sending unlimited Δ assistance to the beseiged building via the re-inforcement pads.
Δ Alien appearances may start to become limited after approximately 600 spawns.
Alien Appearances
Aliens which can spawn into any alien building: Anthropod, Spitter, Skeletoid, Popper. All other lifeforms will not appear.
Spawn Timer
A global timer for spawn intervals into the current battlescape is usually 40 seconds to 5seconds.

  • If multiple pad-structures are present (typically three), the game will choose randomly which set to use for a spawn.
  • If a single pad-structure contains multiple pads, the spawn-active pad will be the northernmost one (isometric view) or top-left (overhead view).

Combat Tactics And Spawn Camping

  • Ammunition will limit your combat time. Weapons which recharge may be a better option.
  • Alien corpses, not weapons, may clog the pad if they were killed immediately after appearing and will halt further spawns. Avoid killing aliens until they have had a chance to exit the device and move away from the active pad.
  • If large quantities of alien corpses are present, the newest corpse will be removed from the battlescape and will not be recovered.
  • If too many corpses are present on the battlescape, the newest corpse will be removed just before a new spawn is due. If multiple aliens have a chance to roam before being killed, the first alien killed, it's corpse will be removed as well (it is ongoing). Any corpse which has been deleted will not be recovered at mission completion.

Caution: Combat Rating and Equipment Captured may not be correct at mission de-brief screen if corpse deletion was implemented or massive quantities of exotic items were dropped and left on the ground. This is a minor error.


Raiding an alien building for agent equipment is possible if escape from the battlescape is chosen instead of completing the mission objective. Agents should fill their inventory with stolen equipment since offloading items is only possible by returning to base.

  • Using aimed-shot with recharging weapons is preferred. The less equipment you bring, the more inventory space you'll have to fill!
  • Toxigun ammunition will be used up when fighting which empties your inventory. To sustain an ongoing battle, pick up Devastator Cannons and avoid explosive weapons.
  • If exotic equipment is increasing quickly from dead aliens, destroying some orange-pads will limit alien spawn spot positions but may also destroy dropped items. Having one kill-squad covering one orange-pad-device allows unused agents to collect dropped loot.
  • Destroying all but one orange-pad-device allows more agents to cover one location instead of three. This may be a tactic to use at the start of the raid.
  • Spawning aliens are easily ambushed (avoid clogging the spawn pad) since they appear one at a time and in an unlimited Δ quantity.
  • A stray shot may hit an explosive plant and cause a chain-reaction with dropped explosives, destroying your loot.
  • A line-up of troop-transports raiding-one-after-another method is suitable to maximise booty and to have all agents gain combat experience and attribute increases.
  • The alien building can be raided endle$$ly!

See Also