Invasion

Invasion is a gametype that was first introduced with the Epic Bonus Pack for Unreal Tournament 2003. The gametype was retained in Unreal Tournament 2004. It is played on Deathmatch maps. It features human players who have to defend themselves against incoming waves of monsters from Unreal, earning points by killing these monsters.

Monsters on the enemy team include: Flies, Mantas, Pupae, Gasbags, Krall, Skaarj, and Warlords. None of the Return to Na Pali monsters appear. Krall appear as usual and Elite Kralls, while Skaarj appear as usual Skaarj, Ice Skaarj and Fire Skaarj (Fire Skaarj use the Skaarj Scout textures of Unreal).

When the game begins, the human team gets some time to gather weapons, ammo, and other power-ups. After a count-down, the first wave of monsters appears, spawning at regular player starts. When all monsters have been killed, the count-down immediately restarts, giving players the chance to restock, after which the next, stronger wave comes. The monster configuration can be changed by the server's administrator, but generally Invasion starts with only weak monsters, with stronger ones appearing in the later waves. Higher difficulty levels also makes them faster. This process repeats until the human team is defeated. It is possible to win, but by default the last level of Invasion lasts for a very long time and huge amounts of Warlords are spawned. When all the players are defeated, the announcer describes the match in one word, like "Slaughter!".

Once killed, a player cannot respawn until the current round has ended. If all players are killed, the game ends. Usually only two bots are allowed to play when playing offline, but online there can be as many players as needed, either real players or bots.

It is possible to play Invasion with the Instagib mutator, removing a large part of the challenge because the Instagib Rifle kills even the stronger enemies with just one shot. However, relatively weak enemies such as the Fly will now pose a greater thread due to their small size, which makes them hard to hit with the thin beam. All of the health pickups are removed in this mode, making the players rely only on the adrenaline Booster combo.

Fans have created custom maps with fortified areas designed to let players be able to defend themselves better. Invasion-inspired mods have also been created.