He works well with effects like Infect and proliferate, and with the right board state, he can combo off and wipe out all opposing creatures or even reduce every opponent's life point total to 0
That already existed on a three-drop 1/3 with double strike printed years ago called Prophetic Flamespeaker that dominated tables
Abilities that count your devotion to black get more powerful based on the number of black mana symbols among the mana costs of permanents you control, including hybrid mana symbols like the one on Rakdos Cacklerperfect for a deck with only black cards
She crash lands, busting a Commander, threat, or problem land like Nykthos or Urborg
Cast it on the turn you intend to go off and your opponents will have a hard time stopping you from taking the game
Now, that said, theres a balance to be struck between things are fine with most play and things are unstable with high-level competitive play that we havent currently hit
