The Alien Fortress Assault, codenamed Operation Leviathan, is the final storyline mission of XCOM 2. The mission is unlocked immediately after the ADVENT Network Tower Assault (Operation Empty Mask). Unlike the Network Tower Assault, this mission is only one of two missions that allows the Commander to deploy wounded soldiers into combat, and the only storyline mission that allows the Commander to do so. After this mission is unlocked, all other activities on the Geoscape become permanently inaccessible - players cannot take on any new missions or conduct any more activities.
The players must make their way to the Psi Gate at the end of a map, defeat the 3 Avatars controlled by the Elders, and keep the Commander's Avatar alive to complete the mission. Success will end the game, while the Commander's death will lead to automatic failure.
- Assault the Alien Fortress (Geoscape only)
- Commander's Avatar must survive.
- Destroy the Avatars.
Immediately after the completion of the ADVENT Network Tower Assault, the mission will be unlocked as soon as the Commander enters the Geoscape. Proceeding with the mission will bring up the Skyranger deployment screen, while cancelling the mission will close the Geoscape.
After the squad has been selected, a cutscene will play, in which Tygan injects Elder DNA into the Avatar stasis suit which the Commander is in. Bradford leans over and tells the Commander to "give them hell." After the synthesis is complete, another cutscene will play with the in-game soldiers saluting the Commander as they walk through the psionic gate.
Along with the squad chosen, the Commander's Avatar also joins the squad on the mission. They are controllable with the same abilities as a Psi Operative, with the added bonus of Mind Control (a 5 turn cooldown). The Commander's Avatar has 18 HP, a Psionic Repeater (which can't be given to any other soldiers), 100 Aim, 150 Will, 25 Dodge, and 250 Psi Strength. The Commander's Avatar also has two hidden abilities: Avatar Regeneration (HP regeneration) and Mental Fortress (immune to mental psionics). Mind Control will always succeed because the 250 Psi Strength grants a 200% success chance.
30-35 enemies will be present on the map before the discovery of the Avatars, and the squad must fight their way through them. After the Avatars are discovered, they will summon 3-4 enemies per turn, meaning that there could be up to 50 enemies on the map at any time.
The Commander and the squad must defeat all 3 Avatars to destroy the Avatar Project once and for all.
- This is the longest mission in the game, with some playthroughs lasting over 2-3 hours because of it.
- After an Avatar is discovered, 3-4 enemies will be summoned each turn.
- As this is the final mission of the game, winning will lead to a victorious Game Over, while the death of the Commander's Avatar will instantly terminate the mission.
- Even if all soldiers except for the Commander's Avatar are dead, the mission will succeed if the Avatars are destroyed.
- No items are collected on this mission - picking up loot is fruitless as it will be discarded upon the ending cutscene.
- After the ending cutscene, the mission will immediately end and grant a "Victory" ending.
- In War of the Chosen, if the player has not yet defeated any of the three Chosen, they must do so in the same area that Operation Leviathan takes place in.
- The name Operation Leviathan is a reference to XCOM Terror From the Deep's ultimate sub the Leviathan.