Katara, Bending Prodigy

A draw engine that runs on tapped permanents and gets larger for having been used: that combination is what makes her more than a fragile three-drop body. The activation cost of looks prohibitive until you read the reminder text, which lets you tap your creatures and artifacts to pay apiece. That converts "spend six mana" into "tap the board you already have," rewarding a wide position where dorks and mana rocks would otherwise idle after combat. The end-step trigger ties the pieces together, but its sequencing carries a wrinkle worth respecting: the intervening "if" checks whether Katara is tapped at the beginning of your end step, so she must already be tapped when that step arrives. Grow her by attacking, or by activating her draw during your second main phase before the end step begins; a choice made during the end step itself comes too late. That makes her one of the rare creatures whose card-advantage engine and combat clock feed the same tapped state instead of competing for it, and tapping her toward a draw is less a cost than a fee she partially refunds, since she returns larger for the trouble. The counterweight is defense: every permanent committed to the draw is a permanent that will not block, so digging off a full board means lowering your guard the turn you dig, and a 2/3 does not survive an untapped race on its own.