I haven't, but it is generally very easy in RMU.
The stats are relatively easy to convert. I would say +3 or +4 Presence (corresponding to Charisma) and then +2 to Reasoning and/or Empathy (Empathy doesn't really sound like it would fit, but Int in D&D is the spellcasting stat for its version of Essence, so that's why I'd lean to Empathy).
The feats are a little more complicated, depending on what version of 5e you are converting from. But you can look to RMU's talents and their costing for guidance. Darkvision and resistance to fire are in RMU already, so just use their costs. Darkness is also an RMU spell, so you could make that into a talent.
I'm not sure if there is an RMU talent precedent for something like Hellish Rebuke, but you could look to the sorts of fire auras that creatures have in Creature Law. Those are talents that have a cost as well.