So I’m sure most (if not all) players here are familiar with the Diablo series and Kanai’s Cube. I have a suggestion for a similar concept. This will revolve around completing the Empowered Monolith’s. Each time you complete 1 of the 3 empowered monoliths, you can destroy any unique/set item you have to select a permanent passive buff for your character. You can have 1 armor, weapon, and jewelry/relic buff at a time. You only get to pick 1 power per run so you must prioritize your choices and be prepared to complete all three empowered monoliths.
The buff itself can be selected from any of the stats of the item, and will match the strength of the stat on the specific item you sacrifice (if it’s a stat that varies).
Take Eye of Reen for example. You destroy the sword and have the option of the following:
1.25 attack speed (with this I’m sure it would have to be changed to a flat % boost like 25%)
+33 Melee Physical Damage
+39 Melee Fire Damage
192% Chance to Ignite
Reen’s Ire buff
By taking the Ignite chance for instance, and then using another Eye of Reen as your weapon, you could effectively earn potential of 400% ignite chance depending on the luck of your drops.
This will allow for a further level of customization per character. Each subsequent run will reward you with the chance to change (or enhance your current selection with a better rolled item) one of the powers. While the current passive buffs received in the Monolith are nice, none of them are really specific to your character as they are mostly passives to drop rates. They don’t really add to the overall power of your character, so something to this effect could do the job.