Tezzeret, Agent of Bolas

The first planeswalker built explicitly to reward a board full of artifacts, and the one that turned "artifact count" into a wincon stat. The +1 is a card-selective dig that ignores everything but artifacts, so it only earns its keep in a deck where the top five reliably hold one; the design makes you commit to the theme before it pays you. The minus abilities are where that commitment cashes out, and both spend loyalty to do it. The −1 hands you a 5/5 body off any artifact (a token, a Signet, a leftover Sword), a finisher that also extends your clock the turn the planeswalker lands. The −4 reads its life loss off twice your artifact count, a number that snowballs from modest to lethal faster than most ultimate-style abilities, and it is the rare drain that scales without ever asking you to cast another spell. But it enters with only 3 loyalty, so the closing blow is a turn or two away: you spend the early activations either digging or building loyalty toward the kill, which is the friction the design wants. What makes the card sit oddly in the artifact-matters lineage is that it leans Dimir rather than mono-blue or the colorless Urza-style engines that usually own this space: the black half does the closing work, the blue half the digging. In a deck without artifacts it does nothing remarkable; in one that hits its theme, it is a snowballing aggro anchor that only needs time.