Urza, Lord High Artificer

The mana engine is the whole trick, and it's built to fold in on itself. That tap-an-artifact-for-blue ability turns every artifact you control into a mana rock the moment Urza resolves, and the 0/0 Construct token it makes on entry is itself an artifact that scales with every other artifact you've deployed: so the card arrives, immediately hands you a source of blue, and grows a body sized to how developed your artifacts are. The 1/4 body was never built to attack; the toughness just keeps Urza alive long enough for the engine to run. The activated ability at the top of the curve is what the mana was always pointed at: an impulse-draw off the top of your library that lets you play the exiled card for free, spells and lands alike, repeatable as long as the artifacts keep producing blue. What makes the design coherent is that each piece feeds the next. The token needs artifacts to be big; the artifacts make the mana; the mana plays free cards off the top; and any artifact you flip into for free deepens the mana pool and swells the token again. It is a self-reinforcing loop stapled to a creature, and the fact that all three abilities want the same resource (artifacts on the battlefield) is what turns a fair-looking rate into a value spiral that snowballs the moment the board is even slightly developed.