darksiders 2 game difficulty and obscure necklace (Darksiders 2)

can anyone tell me what is the difference between the game difficulty in darksiders 2 other than the game difficulty itself. because I heard that there is also a difference in the levels of the Persian 20 lvl 25 lvl, etc. . and one more time Vulgrim gave me a talisman for 40 lvl. and in total the Persian has 30 lvl how to understand this?