Phyrexian Arena has been the staple for Black card advantage for a really long time
There are really two cards in the running for most broken
Archaeomancer Cache Raiders Walk the Aeons What do I need to start this combo
The first card was one of the high-profile creatures from Limited Edition (Alpha) , Lord of the Pit
Fling that monster kitty at the opponent's face, or the more traditional way of just giving that kitty some claws with Rancor so it just runs right over the oppositions chump blockers
If youre feeling particularly devious and like to force your opponents to do some obnoxious math, run Twinflame Tyrant alongside other damage-modifiers, like Torbran, Thane of Red Fell, Mechanized Warfare, or Jaya, Venerated Firemage, then chuckle to yourself as theyre forced to put those damage-modification triggers on the stack in the correct order to minimize the total amount of extra damage dealt