Purge mode is a new mode introduced in the seventh update of SAS: Zombie Assault 3. The goal in this mode is to destroy all the zombie nests and the remaining zombies after destroying the nests. The game says to destroy them as quickly as possible before it becomes too powerful, however, if the player "farms" the nest, or lets it become too powerful, he/she earns more XP and more cash.
In the first "round" of Purge there is only one zombie nest which spawns all the zombies:
- Swarm Zombie (Common)
- Sprinter (Common)
- Choker (Common)
- Shadow (Uncommon)
- Butcher (Uncommon)
- Mamushka (Rare)
- Devastator (Very Rare)
The second Round of purge has two zombie nests which spawn the same amount of zombies (7-10) until one of them is killed, then the remaining nest spawns all the zombies again (14-20). Also the second round has more of the stronger zombies (Butchers and Mamushkas) but Devastators are still rare to spawn.
The final round of purge has three zombies nests which act like in the second round; they all spawn the same amount of zombies, until one nest is killed. Then the zombie count is split and added to each remaining nest, e.g. each nest spawning eight zombies, one gets killed meaning that the remaining nests now spawn twelve each (8/2=4 added to each). Then when the second is destroyed the last nest spawns all the zombies again. The third Round has an increased Devastator-spawning chance as well, so don't stand too close to the nest.
It is helpful to notice that zombie nests can slowly or quickly increase the amount of zombies released; if a nest is left untouched, the nest almost always ramps up the amount of zombies produced quickly. If a nest is left almost dead, it will definitely release many zombies at once.
Power-ups spawn in Purge mode extremely fast, so it is a great mode if you want to kill zombies with only power-up weapons.
'Rush purges' occur when a high ranked player with premium weapons is in the game. The high ranked player may use the premium weapons to take out the nests quickly, leaving nothing for the other lower ranked players to do. It is recommended that players don't pair up with high ranked players with premium weapons in order to get more cash and XP.
SAS: Zombie Assault 4
Purge Nests appear in SAS: Zombie Assault 4, in the Zombie Pods mission, and on a couple of Nightmare Missions. While they spawn zombies and need to be destroyed, they're not exactly the focal point of the mission, as there are other objectives to complete. They are much easier to destroy and spawn zombies much slower than in SAS 3.
Unlike the Purge Nests in SAS3, players have to destroy the purge nest by shooting down each brain section on the nest rather than shooting anywhere on the purge nest.