Iron-Barb Hellion

Pure beatdown math, no upside. The "can't block" clause is supposed to be the discount that pays for a hasty body, the vanilla-plus penalty early designs leaned on to keep aggressive creatures honest. The problem is that the rate never gets paid: six mana for a 5/4 is not a bargain even before you factor in the drawback, so you are absorbing a penalty without the cheap aggression that makes the trade worth taking. Haste turns it into a six-mana Lava Axe with legs, five damage to the face that the opponent can chump or trade with at leisure, and the inability to block means it does nothing at all on the turns it is not attacking. By the point in a game where you can spend this much, a creature that swings for five and folds in front of any blocker is answering a question most decks stopped asking three turns ago. The drawback-for-aggression template has produced genuinely strong cards (Ball Lightning trades durability outright for an immediate haymaker), but those work because the cost is low and the damage lands now. Stretch the same exchange to six mana and the equation collapses: you are paying a top-of-curve price for a body whose entire identity is that it cannot defend you. A clean illustration of why a penalty that is trivial on a one-drop becomes a deal-breaker five mana up the curve, where the durability you gave up is exactly what a creature at that cost is expected to provide.