Forensic Gadgeteer Every time you cast an artifact, Forensic Gadgeteer rewards you with a Clue token
Black (B) seeks power through opportunity, and represents death, free will, and self-interest (though not necessarily evil)
Toby, Beastie Befriender does a lot of stuff right, and it works well with populate, blink, tokens, and more
As you can see Umbris is a 1/1 Nightmare Horror for five mana that's pretty easy to cast in Dimir decks and gets +1/+1 for each card your opponents own in exile
Heliod's Intervention Once upon a time this slot would've been occupied by former Commander mainstays like Return to Dust or Crush Contraband, but Heliod's Interventions ability to scale up and hit more targets (or gain life if necessary) is well worth losing the ability to exile said targets
In the world of Commander and eternal formats, self-mill has potential to be a great primary engine