Theres a tough balancing act in finding the right number of black cards to make sure you can evoke Grief on the first turn, but playing weak cards just to add more black cards to the deck is not something I really want to do
Teferi, Master of Time has become a sought-after card among control players, and its seen a bit of play in both Standard and Pioneer
Kiki-Jiki, Mirror Breaker [The Infinite Loop Engine] Kiki-Jiki, Mirror Breaker has been enabling absurd board states for years
Probably works best in Group Pain decks like Mogis, God of Slaughter and Rakdos, Lord of Riots, though those decks have access to Black so you already have great card draw
When paired with any 1-mana accelerant, say, Llanowar Elves, it becomes a massive threat that must be answered
Centering is one of the factors that a cardholder has no real control over