Groundbreaker

Six power with trample and haste, swinging in on the turn it lands, and the bill comes due immediately: this is rented damage, not owned. The end-step sacrifice is the entire transaction. You pay three green mana for one attack with a body big enough to push real numbers through almost any blocker, and then the creature evaporates before you ever untap with it. That collapses the card into something closer to a creature-shaped burn spell than a permanent: a one-shot threat that happens to interact with combat math and any "deals damage" trigger rather than going straight to the face. The design lineage here is the Ball Lightning idea (a fragile haste beater that exists for a single turn), reworked into mono-green and built around trample so the damage gets through even into a chump. The one toughness keeps it honest, since a single point of first-strike damage or a pre-combat ping turns the attack into a whiff, and the self-sacrifice means there is no way to bank the body for a second swing without outside recursion. It rewards a deck that wants the most damage possible per mana for exactly one window, which is a narrower ask than its raw power suggests, and a more honest one.