Razorjaw Oni

The static ability points at the wrong axis to be useful, and that misalignment is the whole curiosity. Telling black creatures they can't block is a global effect with a clear aggressive intent: strip the opponent of defenders so your 4/5 body, and the rest of your team, can swing into a board that can't stop them. The catch is the word "black." This is a mono-black demon, so its own side of the table loses the ability to block right alongside the opponent's, and the creatures it shuts out of combat are left fully untapped and free to crack back on the following turn. The result is a symmetrical handicap dressed up as a one-sided weapon, and it only tilts in your favor if your opponent leans harder on black than you do: an unusual deckbuilding bet for a black card to ask its controller to make. The era this comes from was full of these tribally tuned spirits whose abilities cut both ways and demanded you build around the cut. Set against a clean one-directional evasion granter, this is the design that trusts you to engineer the asymmetry yourself rather than handing it to you. The 4/5 frame survives most early combat and trades up against a lot of midrange bodies, so the rate isn't the problem; the ability is a puzzle box that rewards a board state most black decks will never naturally reach.