Hmm not so sure we really need more monsters but I did propose adding the Butcher in a special Forgotten Tower that is accessed via Cube Recipe. Namely Wirt’s Leg + Tome of Identify(to play off the Secret Cow level recipe). Instead of warping to an area with lots of Cows, you basically warp to a mini mock-up of Tristram’s Cathedral(Diablo 1 themed) with various Diablo 1 foes along with an occasional Cow MOOOTIVATED to attack you. At the BF5(level 5), you’ll have a layout similar to the Countess but instead of facing her, you’ll face the Butcher. He’ll be Fire Immune, have Holy Fire and Blaze skills to go along with an effective Stun that will allow him to hack and slash until you’re slaughtered beyond recognition. I didn’t think of what he would drop so feel free to get creative here.
My ideas ← in case you want to take a look.
I do want to note though that Crown of Ages(aka CoA) DOES NOT NEED A BUFF. CoA is one of the best Helms in the game for what it yields… it does not need more OP stats such as CBF or Crushing Blow. You do that and no one in their right mind would use anything else since a double Ber CoA can give up to 31% DR(that’s godly from Helm slot) while double Um or 15/15’s can give upwards of 60 All Resistance(which again is godly from the Helm slot…).
Also Obsession needs more than what you’re proposing. You’d need upwards of 15-20% Cold Skill, 20-30% Fire Resistance and 20-30% Lightning Resistance for it to remotely be competitive with 1-H/Shield set-ups. The MF part isn’t really needed either save for what you get from Ist.