Again, look at the XGtE at the Warlock of the Archfey.
11 HD. 1 6th level spell and 3 5th level slots. Clearly based upon an 11th level Warlock. CR 4. This reflects the modern valuation as applied in a recent book to the specific class in question, rather than the valuation placed at the start of the edition on 'monster' builds for other classes. As we posit that Lorenzo is 9th rather than 11th, CR 3 or 4 would seem to be appropriate. The Warlock of the Fiend has an error on the hit points, but it built off a 17th level warlock spellcaster. It is CR 7. Now, it is possible Lorenzo is 17th level - we saw nothing that ruled this out... but that seems unlikely.
Lorenzo is likely an oni - a CR 7 creature. The hints to this are compelling.
And as for your 'three strong', had Matt known that Not and Keg would be 'offline' for the combat, then you'd build for three PCs... but as far as he knew, he was building for 5. My point is that he built a reasonable, but tough, challenge. With surprise and good tactics, it was very winnable (assuming we have the right power levels for the bad guys in mind).
If they start with a stun, stab, and spell on Lorenzo, he likely never gets off a spell or attack (again, assuming he is ~9th level).
I actually don't disagree with that - except, I think, as already stated - Lorenzo was a higher CR than you are giving him. Had they been luckier on their rolls and had they been at full strength - well it may have been different. But that's not what happened and they lucky to have escaped as intact as they did.
Last edited: