Invasion

Invasion is a mission type that allows players to team up together with the Corpus or the Grineer to work against the opposing factions, as a faction invades a specific mission sector. It was first introduced in The Gradivus Dilemma and officially added to the game in Update 11.3. The Infested also are able to invade, although players cannot side with them.

Mechanics
Invasion Missions are essentially a modified version of Exterminate where players are ordered to clear out the level of an enemy faction, depending on who the player chooses to side with. During the mission the player is aided by the faction they sided with (i.e. siding with the Grineer will give you Elite Lancers and Heavy Gunners, among others) as they attack the enemy.

Any ongoing invasions are listed in the Operations window, with the Invasions tab located between the Alert and Syndicate mission tabs. Alternatively, players may select planets with the symbol of the attacking faction to view the contested sectors.

Both sides offer payment for supporting them in contested locations. Selecting a conflict location will present a choice of sides and their respective battle pay, ranging from large Credit sums, to rare Blueprints and Resources.

You will need to commit to a single side to earn battle pay by completing 5 missions, with switching sides eroding your rating with the opposition and denying players either reward. Bear in mind that completing more than the required amount of missions will not increase or improve the reward by any means.

The attacking faction is represented on the left, with a percent of capture. The faction being attacked is represented on the right. Once either side reaches 100%, the invasion ends and the node returns to its regular mission type.

Corpus and Grineer invasions feature only the Exterminate mission mode, while Infested have Exterminate, Defense, Survival, Mobile Defense, and Assassination missions.

If the player is ambushed by any Assassin or Syndicate Death Squad during an Invasion mission, allied NPCs will aid the player in fending them off, even if they are from the same faction (The Grineer will attack The Grustrag Three, for example).

Infestation Outbreaks
Infested missions were largely cleared from their Solar Map locations in Update 11.3 and replaced with Operations using the Invasion mission mechanic. During which, the faction being invaded will assist you in dealing with the Infested threat. Unlike standard Invasions, the threshold for rewards is completing 3 battles instead of 5. Infestations also spread between sectors much faster than Grineer or Corpus invasions, and can often see an entire system covered with Infested missions fairly quickly.

Infested Invasions will always inherit the sector's mission type if the pre-existing sector was Exterminate, Defense, Mobile Defense, or Survival. If the contested sector mission type was not one of those, the game will decide randomly out of those 4. Assassination mission types use Phorid as the assassination target.

Tile Sets
Invasions on Corpus Ship and Grineer Galleon tilesets feature unique map tiles that connect the two opposing vessels of each side, serving as a transitional tile from one map tile into the other, i.e. changing from Grineer Galleon to Corpus Ship and vice versa. Each invasion sector has its own variant of these connecting tiles, which does not change for missions performed on that tile until the invasion ends.

Variant A features a large asteroid mining base connecting the two ships, with plenty of open space and side paths for large engagements. This tile features an energy field that blocks the main path that must be dispelled by hacking a nearby control console. Alternately, there are hidden paths accessible only by parkour that allows players to bypass the field completely.

Variant B features a direct connection between vessels by a Grineer boarding tunnel, leading to a heavily damaged Corpus room.

Variant C is encountered when siding with the Corpus on certain invasions, which features an access tunnel that periodically pulses with energy that can damage player shields. This tunnel exits into the outside of the Corpus Ship that is exposed to space, draining player shields the longer they stay. This then leads to a large glowing portal which transports the players directly into the barracks complex of the opposing Grineer Galleon.

Finally, Variant D is encountered on the same sectors as Variant C, but when siding with Grineer instead, involving a large room with massive cannons firing boarding pods. Players can board an empty pod and initiate the launch sequence by activating the control console inside; this closes the pod, which after a few seconds is fired directly at the opposing Corpus Ship. After the transition, players can exit the pod into the Corpus Ship via a breach made on its hull.

Note that both Variant C and Variant D prevent backtracking into the allied ship as both their transition areas only allow one-way travel.

The Gradivus Dilemma featured an additional variant featuring an asteroid cave connecting the two ships, which has been implemented in standard invasion missions with the Grineer Asteroid tileset as the main tileset.

Infestation outbreaks on Corpus Ships also feature a unique transitional tile, which takes place on a large shuttlebay with an equally large glowing portal at the end, that transports players into another ship. These missions also feature a unique starting tile, which holds a secret room inside an elevator shaft.

Aftermath
Once a victor for a sector has been decided, the player will receive their reward in the inbox regardless who won the sector. However, the player will attract the attention of either the Zanuka Hunter or The Grustrag Three depending on who he or she sided with in Grineer/Corpus invasions (The Zanuka Hunter will attack players who supported the Grineer and vice versa) and may be ambushed during a later mission. Players may also get the Stalker's attention by defeating Phorid.

Trivia

 * If Phorid invades, it will list Phorid as the 'Faction', not the 'Target'. It is also called Phorid Manifestation.
 * The diorama for Corpus invasions contains a graphical error; Flux Rifles can be seen firing as if they were Deras.
 * If the player is playing an unaffected node on a planet that is under siege, the invading enemy can appear in the mission. This does not affect the goal of the mission.
 * Prior to Update 14, the faction that won a contested node would take over that node, replacing the previous faction owner as a result. This may have been removed to avoid disrupting mod drops on a planetary scale (one infamous case had all of Europa taken over by the Grineer).
 * Invasions are a good time to codex scan the faction you are sided with, as they will hold still while not attacking.
 * Invasions also seem to have a higher chance to spawn Rare containers, many users reported finding rare containers especially on invasions.

Bugs

 * The Grineer Breach Pod tile is prone to bugs due to moving parts, especially when playing as a group, most likely due to synchronization errors. Often the players' pod won't load into the launcher. There is no discernible player-made cause for this.

Invasion