Natural Selection Annex

The  or Creature Slaughter Dome is another Circle of Slaughter map. It is located to the right of the vending machines after entering the first structure in the Wildlife Exploitation Preserve with the collapsed telescope. It can only be accessed by a pre-order copy of Borderlands 2 that comes with a special key for the DLC. Entering without it is still possible if a preorder owner's game is joined.

The arena itself is a mixture of all animal habits in the Wildlife Exploitation Preserve, featuring slag ponds and stalker goo as well as varkid hives and skag holes.

Inhabitants
Allies
 * Captain Cabrera

Enemies (during arena rounds)
 * Skags
 * Spiderants
 * Varkids
 * Bullymongs
 * Stalkers
 * Threshers

Creature Slaughter: Round 1
The round starts with a skag and a spiderant wave, the remaining waves are skags and spiderants simultaneously. On normal mode, the enemy level is 25. The round ends after 3 waves.

Creature Slaughter: Round 2
The second round consists of skags and varkids, mostly with level 26. The round will end with after killing a super-badass varkid in wave 5, even if there are other enemies left.

Creature Slaughter: Round 3
This round has mostly skags and spiderants ranging from level 27 to 29, but in wave 2, Bedrock Bullymongs will make their first appearance in normal mode. Similar to Crystalisks, they should be killed with critical hits, as their bodies are almost immune to physical damage. The round ends after 4 waves.

Creature Slaughter: Round 4
This round's enemies are a mixture of varkid, skag, spiderants and additionally, threshers and stalkers with levels of 28 to 30. Special caution should be paid to elemental badass skags, who can buff regular skags with elemental capabilites as well. The round ends after 4 waves.

Creature Slaughter: Round 5
The final round holds a mix of all creatures with a level of up to 31. The most notable enemy here is a badass Pyre thresher. A good strategy is to shoot the critical hit zones of it's tentacles with high fire rate SMGs or shotguns. As a reward for completing the final wave, you will receive Miss Moxxi's Creamer, a rocket launcher that converts some damage dealt to health.

Challenges

 * Cult of the Vault