People were for some reason not really seeing this inside the main guide or the Achievement Trading Thread, so here it is again. Hopefully this will cut down the number of questions here in the sub-forum.
+Estimated achievement difficulty: 1/10
+Offline: 2 (100)
+Online: 3 (150)
+Approximate amount of time to 250: 10-15 hours (depends on how much fortification upgrading you need)
+Minimum number of playthroughs needed: 1
+Number of missable achievements: None
+Do cheat codes disable achievements? No codes
+Does difficulty affect achievements? Only "Kill Locust (Like a Boss)"
+Glitchy achievements? None
+Unobtainable achievements? None
+Extra equipment needed? No
Step 1: Hosting and Like a Boss
Find a group of 3-4 other players with the DLC (two people can have second accounts if you can only get a group of three) to do "The Host With the Most," "Places to See, People to Destroy" and "Kill Locust (Like a Boss)."
Step 2: Upgrade Fortifications
Use the method described in "What Does This Button Do?" to upgrade your Spikes, Turrets, Silverback and Command Center to their max levels and get 500 kills with the Silverback's rockets.
A very quick and easy set of DLC achievements. The grinding to unlock the Silverback rockets will take the majority of your time.
The Host with the Most 25
Host a private Horde Match with a party of 5 players on any Horde Command Pack map (any difficulty).
You can host a match on the DLC maps with any number of non-DLC owners joining you, so you don't technically need to find other people with the DLC to get this achievement. The people who join will not be able to earn the achievement though. To unlock the achievement, you need to complete at least one wave on any difficulty with all five players in the group.
I would suggest finding four others who DO have the DLC, or as few as two others if two people sign in second accounts (press on your second controller to sign in a guest), and get "Kill Locust (Like a Boss)" at the same time, hosting and completing one of the boss waves on Hardcore difficulty using all Onyx Guards. The other people who need to host just need to get everyone in and finish a wave on any difficulty, then you can quit out and repeat for everyone else. May as well do "Places to See, People to Destroy" with the same group hosting Beast matches.
This needs to be done on either Blood Drive, Rustlung or Azura.
Places to See, People to Destroy 25
Host a private Beast Match with a party of 5 players on any Horde Command Pack map (any difficulty).
See "The Host with the Most" for more information.
What Does This Button Do? 50
Get 500 Silverback rocket kills in Horde (any map, any difficulty).
You'll first have to upgrade your barriers to Level 7 by spending $120,000 on them to unlock the Silverback itself, then spend another $500,000 on the Silverback to reach Level 3 and unlock the rockets. Then buy the Silverback and use the rockets by spending $10,000 to arm it, planting with the A button and firing with the right trigger to kill any 500 enemies during Horde waves.
Alternatively, you can find a friend who has the Silverback upgraded enough, have them purchase and arm it with the rockets, then use it yourself. Even if you have not spent a dime upgrading a Silverback, the kills will still count.
The easiest way to earn money is using the Solo Horde method with the Friendly Fire mutator on. After every wave, shoot the Silverback and use all your money to repair it. Money spent on upgrades is affected in the following ways:
Mutators take off/add the same amount as their percentages for experience. So it would be -25% for Infinite Ammo, +5% for Friendly Fire, etc.
It's Hammer Time! 50
Achieve Level 4 in Horde Command Center fortifications.
You'll first have to upgrade your Turrets to Level 8 by spending $360,000 on them to unlock the Command Center itself, then spend another $40,000 on the Command Center to reach Level 4 and unlock the Hammer of Dawn. See "What Does This Button Do?" for information on upgrading fortifications. Unfortunately the Command Center can not be damaged with Friendly Fire, so it is best to buy it and then die and restart from the beginning of Horde to keep purchasing it. If you play on Thrashball with a second controller (give its money to your main profile) you can buy two Command Centers per round.
Kill Locust (Like a Boss) 100
Defeat a Boss Wave as 5 Onyx Guards (Hardcore difficulty).
Obviously Wave 10 would be the easiest for this. Feel free to use mutators to make it even easier (Infinite Ammo and Super Reload being the best, along with Instagib Melee) and skip right to Wave 10 so you only need to play the one wave. Make sure you have a full party of five players (can be as few as three real people with two guest accounts), you're all using the proper Onyx Guard skin and you're on Hardcore difficulty.
May as well get everyone "Host with the most" and "Places to See, People to Destroy" with the same group. Make sure everyone gets a turn!
Note: You must be alive at the end of the wave to unlock the achievement.