Beast Quest

Shadow Marks are stronger versions of enemies that will spawn once their associated quest is obtained from one of the bounty boards found in the game's towns. Generally, the enemy will be in the same zone as the bounty board, but not always. The last few marks will need to wait until beating the third and fourth bosses as new paths will open with the glide ability from the third boss and the lava hardening after beating the fourth boss.

As mentioned in "Hero of Avantia" you can make use of the glitter trail to lead you to these marks, but sometimes it runs you in circles or straight into walls. I sadly did not think I was going to write a guide for this so I didn't take note of where the enemies were, and I apologize for that, but keep traveling to new campsites and using the glitter trail and you should find them all with minimum headache. Try to take note of blocked paths you come across during the story (very large gaps for instance), as shadow marks will usually be found in those locations later on.

Note: I don't know if this was just a weird glitch I encountered or what, but after completing the last mark, my tracker was at 83% and the achievement did not unlock. Thinking I had somehow missed one on an earlier bounty board, I traveled to the forest town, then the ice town, and it unlocked upon arrival in the ice town. No clue why, but try traveling around if you finish and it doesn't unlock right away.