Farming skulls in OMD2 has never been hard.
However, there are certainly much faster and easier ways to get them.
We play on Nightmare difficulty for maximum bonus skulls and on the first Story mode level; The Edge for the shortest game time.

(1) Trapless, (2) Manaless, (3) Untouchable, (4) Perfect Victory
It would be ideal to have all those skull multipliers but you have to forgo "Manaless" if you choose to aim for "Trapless" and vice versa because It is almost impossible to not use both traps and mana.
"Untouchable" is a must-have multiplier on any occasion in order to achieve 15 skulls. Avoid losing health at all costs.
"Perfect Victory" is also a must-have multiplier but not really something to worry about. Make sure no single enemy reach the rift and finish the game before or on par time.

The method of farming shown in the third video is the fastest way to achieve 15 skulls, yet the trade-off is that it requires the most effort with controls compared to using traps or guardians. What the first two videos demonstrate are relatively easier to do in terms of control.

It is advised to have weapons to be more flexible when you are dealing with orcs. Make sure not to use mana costing abilities when you aim to achieve "Manaless" multiplier.

What are skulls? Skulls are what you earn from completing a level. They sometimes drop from dead orcs and you must pick them up and complete the game session to see incremented skulls.
Those collected skulls from each game are used to upgrade and purchase new traps, weapons, etc..

In order to reap a lot of skulls in one game session, you need to play on Nightmare difficulty. In order to have acess to Nightmare difficulty, you must first complete every level of Story mode on War Mage difficulty.

Level: The Edge
Difficulty: Nightmare
Completion Time: 4 Minutes 13 Seconds

• (1) Archer Guardian
  
• (2) Dwarf Guardian
  
• (3) Paladin Guardian
  
• (4) Guardian Trinket
  
• (Optional) Scavenger Trinket

• Do not use mana for "Manaless" (6 skulls)
  
• Do not get hit by enemies' attack for "Untouchable" (5 skulls)
  
• Do not let enemies reach the rift for "Perfect Victory" (2 skulls)
  
• Win the game (2 skulls)

You can also work on achievement: All Aboard (Kill 1,000 orcs with minecarts).

It is totally fine to mix other traps at your own convenience.
You may have to experiment.

Level: The Edge
Difficulty: Nightmare
Completion Time: 4 Minutes 13 Seconds

• (1) Spring Trap
  
• (2) Trap Reset Trinket
  
• (Optional) Scavenger Trinket

• Do not use mana for "Manaless" (6 skulls)
  
• Do not get hit by enemies' attack for "Untouchable" (5 skulls)
  
• Do not let enemies reach the rift for "Perfect Victory" (2 skulls)
  
• Win the game (2 skulls)

I forgot to have an upgrade of reducing trap reset time for Spring Trap when I was making this video.
Therefore, it should be much easier than shown in the video once you have everything upgraded.

Level: The Edge
Difficulty: Nightmare
Completion Time: 3 Minutes 24 Seconds

• (1) Wind Belt
  
• (2) Mana Rage Trinket
  
• (Optional) Polymorph Ring and/or other weapons and trinkets at your own convenience

• Do not use traps or guardians for "Trapless" (6 skulls)
  
• Do not get hit by enemies' attack for "Untouchable" (5 skulls)
  
• Do not let enemies reach the rift for "Perfect Victory" (2 skulls)
  
• Win the game (2 skulls)

Using only Wind Belt and Mana Rage Trinket was first done by HeroClixWorld. You can watch his video here.
https://www.youtube.com/watch?v=GCtE1sKx_u0

I have nothing much to say here. However, just for the sake of completeness, I made this last(filler) section.

Watching the videos without reading a wall of text will suffice hence they are all self-explanatory.

Thank you for reading my guide. I hope you enjoy farming skulls and killing countless number of orcs!






Watch the videos.
Thank you.