I dunne think that XP raises
But it might be so that the game spawns more monsters and thus giving you a higher netto XP rate
But i'm not sure
The essence of the higher difficulty is that they get stronger and you get weaker
not that you get more XP
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All Hail the Seventh house Sorcerer
Master Magician of Necromancy
Prince Rikard T'Aranaxz of Natri'x
Clanmaster and Mental Father of the OHF
Ramanish of Neathan'Calith
High Priest and son of the Eternal Phoenix
Shadowlord of the Silver Shield
Baron of Yusliks
Duke of Gerdran
Duke of Tralixz
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AND!!!
Laughing Hyena!!!