Duskworker

The regeneration trigger keys off the wrong half of combat. Most defensive regenerators want to survive a block, sitting back as a stubborn wall; this Construct only shields itself when it is the one being blocked, which means it wants to attack into trouble and live to swing again. Pair that with the firebreathing pump and the intent reads clearly: a colorless beater built to walk into bad blocks, soak the damage, and grow through them. The 2/2 body is the cost of universal access, an early-era pricing convention where artifact creatures any deck could run carried a premium that showed up as a stat line well below curve for the mana. What you are buying is not the body but the combat math: a defender who simply blocks and deals lethal damage accomplishes nothing, because regeneration replaces that destruction. To actually stop it, an opponent has to reach past the regeneration shield with something that does not destroy at all (exile, a bounce, an edict that forces a sacrifice), or pin down the trigger with an effect that says it cannot regenerate this turn. Short of that, the trade is a non-trade and the Construct survives to attack again next turn, growing each time three mana of any color is left over. It is a grindy, unglamorous engine rather than a finisher, and the three-mana-per-point pump keeps it honest in the late game where any leftover mana counts as fuel.