I dont currently have any decks that self-mill a bunch, but Im definitely planning on slotting this into a couple of my black decks: Doran, the Siege Tower
Birgi, God of Storytelling // Harnful, Horn of Bounty is the only red card Ive jammed into literally every single red deck I own since its release
Court of Grace Court of Grace is a little like Palace Jailer on a stick, but it generates fliers instead of exiling a creature
If any of these see play, I expect it to be this one, but theres a real chance that none of them make it once the craziness of the post- Horizons turmoil settles down
Most likely you'll want to Rush out one of your Merlins, either Goat or Rabbit, and get the value from their on-play and on-leaving-play effects
Someday there'll be a changeling-focused blink deck and Champion of Dusk will be an all-star there as well