Aluren

A symmetry that almost nobody plays straight. The text reads like a generous gift to both players, and the "any player may" clause is doing real balancing work: in theory your opponent gets the same engine you do, so the card sat as a curiosity for years before anyone weaponized it. The break came when builders realized the symmetry only bites if the opponent has free creatures worth casting, and against a focused combo deck they almost never do. The combo deck, meanwhile, is built from nothing but the right small creatures. Pair the enchantment with a creature that bounces another creature on entry (Cavern Harpy is the classic) and a creature whose enters-the-battlefield trigger drains life or generates mana (Maggot Carrier, Wirewood Savage, the right one-drop), and the free-cast clause becomes an arbitrarily repeatable loop: cast, trigger, bounce, recast, all for zero mana, all at flash speed. The flash grant is the underrated half, but its real use is timing rather than tempo: because the effect is symmetrical, you do not pass the turn and hand the opponent first crack at it. You combo the moment Aluren resolves, or in response to interaction on your own turn, using flash to win before anyone else can touch the engine. The mana value 3 or less restriction is the only real wall: it forces the loop to be built from small, specific pieces rather than fat tutorable finishers. The result is a deck that looks like a fragile pile of three-drops until it suddenly executes a combo nobody at the table opted into.