The main easter egg boss fight requires that you activate 3 computers, one is right next to pap, another is behind the bar of castle, and the last is down the stairs to the left of double tap.
(rest of easter egg at the bottom)

I wouldn't recommend starting the boss fight until after you have gotten the keycard to Jug

There are 5 challenges each rewarding a different perk at a discounted price.
1.obtain 5 perks (can be done with quick revive and the other challenge perks)
2.Survive 8 rounds
3.50,000 points (whole game)
4.100 headshots
5.150 kills

There are multiple workbenches:

Monkeybomb workbench is near the challenges

The shield workbench is the one up the stairs near Wunderfizz

The Ragnarok workbench is behind the bar

There is a lot of parts around the map which locations I do not know by heart so I recommend the vulture perk.

Pap needs to be built, there are 3 parts, one in pap spawn, one near Wunderfizz on a shelf, and the last near the teleporter to the left on a shelf.

How to get to pap:

Just activate the teleporter not that hard tbh. (it will cost 1,500 points to use)

Keycard location:

It is unknown where the keycard is and that is a big problem, however I have an idea and it may be my game bugging

Near The banana perk to the left there is a wall that allows you to blow it up with thermite
I was unable to do so but I assume behind that wall is the keycard. The other location I hypothesize is the shack near jug.

Overall this map is pretty buggy and you will likely experience issues that doesnt take it away from being a good map however.

After you are ready and want to finish the map simply activate the secret teleporter and you will be sent to jug, if you do not have the keycard you will be locked in there. After defeating the 5 bosses you will need to pay roughly 40,000 points to escape.

Goodluck and have fun! (also there is buy-able armor which I recommend getting its great paired with widows wine.)