This was the last achievement of the bunch for me and I was curious how it worked so I had a look at the code. It's random, but at least this is a guaranteed way to get it.

If the other guide authors want to copy this that'd be nice, then I'll take this one down.

When you start the game, it picks a level at random and if you finish that level you get the achievement. The game doesn't show which level it is; it can be any of the 6 levels in any of the 4 maps with the exception of the hidden level and the survival challenges.

To be sure you get the achievement, complete these levels without quitting the game in between:

Map 1

• Castle Aldrheim
  
• Disappointing Forest
  
• Cave of Trolling
  
• Swamp of Smells
  
• Badass Beach
  
• Assaultwater Lake

Map 2

• Predictable Plains
  
• Dragonsweat Mountain
  
• Murderdeath Peak
  
• Snowy Snow Glacier
  
• The Forest of All Kings
  
• Scenic Route Road

Map 3

• Nagelfar
  
• Bifrost
  
• Asgard
  
• Thor's house
  
• Valhalla
  
• Party Garden

Map 4

• Gravey Swamp
  
• Niflheim
  
• Helgrind
  
• Hel
  
• End of the World
  
• Afterlife Anomaly

There are some rumours that playing on Normal will increase your changes, that's not true. Also, it doesn't matter if you play online or offline.