In Nightmare and Hell difficulty, you can find veteran monsters near the end of each Act. There are 5 types of veteran monsters, one for each Act.
Note: They don't always spawn so sometimes several runs are needed to find them.
Kill them and receive an 'Evil Eye' token:
|1||Clawstorm Terror|| Barracks|
|2||Fairy Witch||Canyon of the Magi|
|3||Glowing Blob|| Travincal|
Durance of Hate
|4||Landmass|| City of the Damned|
River of Flame
|5||Bane Hunter||Worldstone Keep|
RecipeThis upgrade recipe adds the following bonuses:
+1 to [Your class] Skill Levels
+20% to Experience Gained