Homunculus Horde

Blue has always paid you in cards for drawing cards; this one pays you in bodies instead. The key is a piece of templating that shows up throughout modern card draw: "your second card each turn." That phrase means the natural draw step alone does nothing, so a hand full of these creatures sits inert until you stack an extra draw on top of the one you were always going to take. Cantrips, wheels, and any repeatable "draw a card" effect become token machines the moment they push you past that first draw. Because the second draw can land on an opponent's turn, the copy arrives at instant speed, and because each copy is itself a Homunculus Horde, every body on the battlefield is independently watching for the same window. Two or three out at once, and a single extra draw fans into a whole row of fresh 2/2s simultaneously. The once-per-turn ceiling is what keeps the loop from spiraling: draw a third or fourth card and the trigger has already spent itself for the turn, so board width, not raw card quantity, is what widens the army. What makes the design tick is that it converts a deck's ordinary churn (the extra draws blue was already leaning on) into a growing clock, without asking for anything you weren't going to do anyway.