Circle of Flame

A static deterrent that taxes attackers without ever leaving the battlefield. The damage is small (one point per attacking creature that lacks flying), but it accrues every combat for as long as the enchantment stays in play, which reframes it from a removal effect into a tariff on ground assaults. The clause that does the real work is the trigger condition: it fires only on creatures attacking you or a planeswalker you control, so it punishes aggression specifically rather than policing the board generally. A single one-toughness attacker dies to it for free, an army of X/1 tokens gets shredded on the way in, and even an army of bigger creatures pays an attrition cost over a long game. The flying exemption is the honest part of the design: it does nothing against evasive threats, so it answers the swarm-and-go-wide plan rather than the air. As a two-mana enchantment with no upkeep cost and no activation, it functions as a passive wall that scales with how many bodies the opponent commits to the red zone, which is exactly the matchup a slower deck wants help surviving and exactly the matchup a controlling deck most fears.