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Seb-wejem
I also use enemy skills and abilities to set DCs, the most common is sneaking against the enemy passive perception, but just the other night the players rolled perception against a DC 17 to spot some shadow demons. I sometimes do the same for interaction checks rather than making an opposed roll, I just add 10 to the NPC's Insight or perhaps their own interaction skill. I find that's a good way to set DCs when the players are in interacting with the people of the setting.