Niv-Mizzet, Visionary
Every prior Izzet dragon to carry this name drew off the act of casting: a spell resolved, a point of damage went out at a target, one card came back. This rebuild moves the trigger to the source and lets the size of the hit set the size of the reward. Noncombat damage dealt to an opponent, from anywhere you control, converts one-for-one into cards, so a single face-burn spell refunds itself with interest, a chain of pings pays in a steady stream, and one uncounterable haymaker to the dome can crack the library open in a single motion. The no-maximum-hand-size clause reads as flavor but does real work: any effect capable of drawing eight or ten off one damage instance has to have somewhere to put them, and the two lines are written to be read as one.
The direction of the damage is what keeps this from being a free value machine on any board. Combat is off the table, and the payoff registers only when the damage lands on an opponent, so the 5/5 flier cannot mine its own creatures or turn attacks into cards; it wants damage aimed outward, at players, in quantity. The dragon does not manufacture the burn. It scales whatever burn you already brought, and the deck has to supply the fuel before the engine has anything to draw on.
