Mechan Shieldmate

Defender is usually a wall's whole identity: a body priced to block and forbidden from swinging. This one wears the keyword as a condition rather than a sentence, and the 3/2 statline is the giveaway. That is a genuinely aggressive rate for two mana, offense stats stapled to a defensive keyword, and the gap between them is the entire design. The creature is a wall on any turn you did nothing, and a real attacker on any turn you resolved an artifact, a permission slip that resets each turn and asks the deck to keep feeding the condition. What makes the conditional clever is that it checks for an artifact entering under your control, not a spell cast, so tokens, secondary artifacts off a single card, and free permanents all flip the switch just as well as hardcast metal. The result scales with how artifact-dense the board already is: with no mechanical engine behind it, it is a blue wall; with a steady drip of cheap permanents, it is a two-drop beater that happens to block for free on the turns you stumble. It rewards the exact play pattern blue's artifact shells lean on and punishes nothing when the drip runs dry, since a 3/2 defender is still a perfectly serviceable roadblock.