I noticed there is not another mini-guide for the important two, of course again the other one is if you love playing as a Scout so no problem, I want to share how I got those three but it feels like forever.

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A Year to Remember
Get 2004 lifetime kills.
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• 1. Download this map from Steam workshop: achievement_primecuts.
  
• 2. Launch the map and use your other dummy account.
  
• 3. Any weapons are fine, I would prefer the bat.
  
• 4. Type in mp_respawnwavetime 0 to make the grind faster to complete.
  
• 5. Stay near to where the red team spawns or your dummy account, make sure you can kill your dummy account consistently.
  
• 6. Type in +attack on console and enjoy the afk grind for 5 hours.
  
• Sometimes, even if you set up the position correctly, its best to check as your dummy account will be launched further or to the side.

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T-1000000
Collect 1,000,000 credits in your career.
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Metal Massacre
Destroy 1,000,000 robots.
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The longest and most consuming to grind but here is what you should be doing:

• 1. Download the map from this site: TF2Maps[tf2maps.net].
  
• 2. Boot up the game after completing your map download and files.
  
• 3. The name of the map should be: mvm_achievementgrinder_rc1.
  
• 4. Do few achievements related to mvm if you can, then start upgrading all or just Engineer, wrench, and sentry gun to all max.
  
  
• 5. Now stay close to the bots spawn area where 11-22 spawn infinitely. Build sentry and dispenser close.
  
• 6. Type in +attack on console. Now you can leave the game running for at least +30 hours.

Congratulations, now you just need to wait and reload the map if all gets either laggy or if you want to have the numbers load up.