Veiled Sentry

Sitting inert on the battlefield, this waits for an opponent to commit something to the stack, then animates with a body scaled to exactly what they cast: a two-drop yields a 2/2, a five-drop a 5/5, the size of the threat against you becoming the size of the answer. That self-scaling defense is the unusual idea in a one-mana investment, since most reactive permanents settle on a fixed shape rather than mirroring the spell that provoked them. The drawback lives in the timing. The body only materializes in response to a cast, so it offers no proactive pressure and no value on an empty stack; it is a deterrent that taxes the opponent's tempo rather than building your own clock. And once it animates and the provoking spell resolves, it remains a creature, exposed to the removal that a static enchantment would have sidestepped. That conditional in the trigger ("if this permanent is an enchantment") is what gates the transformation: it only flips while it is still an enchantment, and stays a fragile Illusion afterward. The opponent's decision is the real engine here. They must judge whether resolving the spell they want is worth gifting you a blocker sized to trade with their own threat, or whether to bait it out with something cheap first. A clever bit of early-era design that turns enemy spellcasting into your defensive resource, undone by a rate that demands patience for a body that arrives reactive and brittle.