It took me about 2 or 3 times to understand the mechanics for greed demon and i have won against him (it was such a pain he kept spamming doom gem),now i have completed the game,waiting for more updates for sure!
Make sure ur max lvl (95),invest skill points in arcane and cooldown as much as u can,use brute force against greed demon as much as possible using light magic,get rid of gems by using aoe spellls (specifically doom gem),doing so will make greed demons's mana drain faster ,also really recommend having all potions,light/invisibility,mp/hp regain for backup
So do you use Celestian Celica and then use an invisibility potion and time stop one after another to just do as much light damage to Greed Demon while the gems don't bother you? I already have maxed arcane, speed, and cooldown that I can without using clothes and AoE spells still don't recover fast enough to be relied on more than once per fight, especially because Greed will just cast Doom Gem again the moment I destroy it while still often getting to summon another gem alongside it.