solo scaling, or solo mode option bc the amount of damage i do is usually 10% and it's a pain to solo any dungeon.
just make us deal 3x damage to bosses only and we should be fine.
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I would say add a third difficulty selection that can only be launched while solo. Scale boss health down and enemy health down by a tiny bit, but you wouldn't be able to earn any of the triumphs for the dungeon on this difficulty it would be just to complete encounters and get loot.