Riverchurn Monument is the kind of mill card that scares me, because it tends to combo with a bunch of mill favorites like Bruvac, Phenax, God of Deception, and ways to make players mill a lot of cards (Maddening Cacophony, anyone?)
Breed Lethality, from the Commander 2016 set is a deck I keenly considered for the more competitive options
There are 77 golden chocobos from Final Fantasy, there were 3 (hundred) rings given to the elves, and The Brothers' War Retro Artifacts were the first large scale printing of serialized cards
But then, theres that 5% chance you roll a natural 20 and your opponent will get a 0/1 white Goat token, which will elicit all sorts of Greatest Of All Time jokes at the table
Graveyard hate is also an area in which black excels
even some of the common cards in the Alpha Set are now worth several thousands of dollars