The Leviathan is the sixth boss (fifth in mission order) introduced. It is first encountered in the San Francisco mission.
The Leviathan has four modes of attack that it switches randomly between each time it teleports. It can either fire large spreads of torpedoes, launch a constant stream of missiles, fire a single massive flurry of those missiles, or launch a single nuclear weapon with tremendous damage and area-of-effect. The Leviathan's tremendous offensive power does not hinder its defensive abilities and it is tougher than one would expect.
All Leviathan's projectiles, including the nuclear missile and torpedoes, are able to be destroyed; bringing Gatling weaponry is an excellent tactic for easing the difficulty of the fight. The torpedoes have the same HP as standard missiles, but the nuclear missile has about 240 HP, so it takes considerably more shots to destroy.
The Leviathan does not have an elite variant.
The Burst Fire and Finisher abilities, and the Battlecruiser Heavy Damage ability will destroy the boss in seconds. Note that this requires a good damage build as well as enough speed to dodge the missile attack.
- The Leviathan shares some dialogue lines with the Kraken.
| Fortress Destroyer Enemies
Enemies listed in parentheses () following another enemy are the elite form of that enemy. If there is no elite form listed, that means one does not exist or has not yet been added to the game.