This is accomplished in the Zombie game type playing solo on the level "Five". You must first complete the campaign on any difficulty to unlock the level "Five" in Zombies.

Keep the Defcon level at 4 until we see the professor emerge - once we see him, someone will tap the last Defcon and we will all meet in the Pack-a-Punch room and have some chocolate chip cookies. Whoever sees the professor first will tell the others that he is here, and they will back away from the table - so the chased doesn't get blocked.

This strategy is written specifically for the map 'Kino der Toten'. The method applies to all maps, as long as you know where the Pack-a-Punch machine and Mystery Box locations are. Personally I think the map 'Five' is a better choice for many reasons, so we'll be doing it there.

Firstly, this achievement requires at least two people playing in Zombie mode. Next, you or the other player needs to obtain a crossbow, which can only be found in the Mystery Box which is randomly placed on the map. The weapon you get from the Box is random, so you may have to try several times. After you have obtained the crossbow, you need to head to the 'Pack-a-Punch' machine, which can only be accessed by turning the power ON. The 'Pack-a-Punch' machine costs 5000 points.

In 'Five' the Pack-a-Punch is located in any teleporter after you press all 5 Defcon buttons.

After you have the 'Pack-a-Punch' Crossbow, the other player will need to be shot at with the weapon and the resulting explosion has to kill at least 6 zombies. The best way is to have the person with the crossbow shoot the other player, and have that player run into a group of 6 or more zombies - works best when another player has the Winter's Frost gun to freeze the zombies. A horde of zombies emerges when the Defcon goes from 5 back to 0, that is if you're in the Pack-a-punch room. This is the best time.

See "Big Bang Theory." Secret achievement.

First of all "resurrection" is just the process of someone bleeding out and respawning.

Now to be trapped in the receiving area, both of the excavators must trigger and succeed, blocking off both tunnels and cutting off access to the power room.

When you hear the announcement of your last tunnel being breached, have the person not wanting the achievement go to the Labs half of the map.

Once at least one player is "trapped" on the Labs half of the map, with a crawler, ALL other players must down themselves and bleed out. (Jumping off the cliff is a fun option)

Once all other players are dead, the player on the Labs half of the map may kill the crawler and the other players will "resurrect" near you and they will unlock the achievement.

Also once a player unlocks this achievement, the son Nightmare by Avenged Sevenfold will start to play. Like all other songs it will only play once per game.

**The excavators blocking the tunnels is completely random. As long as the power is turned on an excavator might begin drilling a tunnel. You will know when this happens because a voice will play saying an excavator is drilling tunnel 6, etc.**

Important: This achievement is slightly buggy. Some people are having it unlock randomly when respawning, with no tunnels breached. DO NOT LISTEN to these strategies. Follow the one in the guide to have it flawlessly unlock. Attempting these glitched stragities will cause you to mess up. BOTH tunnels must be breached.

This achievement is much easier than it sounds. You must buy all 8 perks in one game.

Juggernog 2500 Area 51
Speed Cola 3000 Area 51
Double Tap 2000 Bottom Floor of Labs
Quick Revive 1500 (500 in solo) Receiving Room
Deadshot 1500 Second Floor of Labs
Phd Flopper 2000 Biodome by Box Spawn
Stamin-Up 2500 Tunnel 11
Mule Kick 4000 Outside Biodome

For this achievement you just need to have all perk locations open, 4000 Points, a crawler, the hacker and you must teleport to the Area 51 twice.

All you have to do is buy each perk and after purchasing, hack the machine to return the perk and get a refund. Do this with every perk and the achievement is yours.

Note: You cannot easily return Mule Kick, as you do not have much time to hack the machine, as it is outside.

First of all to have 3 guns you must purchase the new perk Mule Kick, which is located outside the biodome and costs 4000 Points. It is advised not to purchase Mule Kick until you have at least 1 PaPed gun and Juggernog.
Once you have mule kick, it is very straightforward. Just buy a 3rd gun after purchasing the perk and Pack-a-Punch them.

The Pack-a-Punch Machine:
To get back to the PaP, ALL players must jump on the teleporter outside the biodome. Once back in area 51 ONE player can safely PaP ONE weapon. After returning the teleporter requires time to recharge.

To get extra time in the PaP area, have the player with the hacker hack the machine to close the gates. If you do this have 1 player throw a gersh or have everybody ready to fight your way back to the teleporter.

This achievement may be tricky as the excavators becoming active is random.

As each of the excavators becomes active you must grab the hacker and bring it to the receiving room. In the receiving room, there are 3 consoles, which will say access denied if you move close to them.

Whenever an excavator becomes active, its console will have a green flashing light on. The player with the hacker must then hack the console to stop the excavator. This action also nets the hacking player 1000 points.

Once all 3 different excavators are hacked the achievement will unlock

Note: Do not break the glass in the receiving room, as this will hake things incredibly difficult for the hacker, as he will have no air!

Hint: If an excavator becomes active again after you have hacked it, just let it dig. It will still count toward the achievement and it will prevent it from becoming active a third time, instead of the ones you need.

First off, to get this achievement at least the host needs the previous easter egg achievements. To play it safe, it is suggested (but not required) that everyone in the party should have them, as lots of people have had different experiences of it not unlocking due to not everyone having the achievements.

Also, this has to be done online, as the Vrill Generator will not appear in solo (splitscreen counts as solo.)

Info: The previous easter eggs are required because you need the golden rod and focusing stone. They are combined together to make the Vrill Generator, so in can be inserted into the slot to power the device.

NOTE: We WILL be doing the Easter Egg a game before trying this achievement. I haven't done the Easter Egg for Moon yet and don't know how to, so there will need to be someone that knows.