This is the Tower Pack, the third DLC with a "horde mode" where your objective is to defeat many humans/Nosalises in a virtual combat simulator until the time ends.
See the description of Xbox Live:
Prepare yourself for the challenge of The Tower - the Metro's virtual combat simulator. Each level is increasingly difficult - can you make it to the top? Compare your time and score against your friends with the added leaderboard functionality and try again. Note: This purchasable item is included in the Season Pass
In this DLC you have 3 difficulties: Normal, High and Huge (Last being the hardest difficulty) and you'll need complete at least 1 level on Huge difficulty. At the start you need to fight against a group of human enemies, in a tutorial mode. After that you'll need pass by 3 hordes and a final horde, following this path:
Horde 1 - Nosalis, difficulty can be Normal, High or Huge
Horde 2 - Nosalis, difficulty can be Normal, High or Huge
Horde 3 - Humans, difficulty can be Normal, High or Huge
Horde Final - Nosalis
Automatic Heavy Shotgun aka Abzats
- Use Claymores whenever you can as they will make surviving the arena easier.
- Also use grenades and whatever else you have in the throwing department.
- By the third wave explosives will have run out so use your weapons as described earlier.
- When harder enemies show up buy both reinforcements to help you make it the rest of the way.
- Defend them with your Gatling as they are your lifeline.
- When restocking ammo make sure all grenades and Claymores are used.
In horde 2 and 3 use Normal difficulty and in the first horde I suggest you pick the Huge difficulty, you can use a trick to "avoid" too much damage: keep running in circles until the time is over, you'll get some damage but you will not die, and you can finish this level and get one achievement.
Finish this level alive and get one achievement:
When you complete the final level you'll get the last achievement of this DLC. Use the tip above about running in circles if you struggle with it:
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