Iron Myr

Red's slot in the original Myr mana cycle has always been the strange one. Each member produces one color of mana, and red is the color that least wants to sit a creature back and use it as a mana battery on a clean board: that runs against everything red is supposed to do. Which is exactly where Iron Myr earns its keep. Being a colorless artifact, it produces red regardless of what your lands make, so it fixes for a splash of aggression without bending the manabase, and it survives the punishment aimed specifically at nonartifact mana sources. The 1/1 frame does quiet work alongside the mana: artifact-creature count for affinity and metalcraft, a sacrifice target, a chump blocker, a Myr for any tribal hook that cares. The fragility is the honest cost. A mana dork that dies to every incidental ping or sweeper is a tempo loss dressed as acceleration, and one toughness is the smallest body Wizards could bolt to a colored-mana rock and still call it a creature. So what you are paying for is not the rate (it does not pay you back until a turn after it arrives, and only one mana at a time) but the optionality of a permanent that is both a creature and a source of red, generated off an artifact rather than a land that would have to be the right color in the first place.