Shantotto, Tactician Magician

Most creatures that pump off spellcasting count the spell, not the mana behind it; this one counts every point of mana that actually goes into the cast. That distinction is doing real work. Kickers, additional costs, an X in the mana value, cost-increasing effects: all of it feeds the +X/+0, and crossing four mana on a single spell refunds a card on top. The framing rewards concentration over volume. One big spell swings the 0/4 hard and draws; a fistful of one-mana cantrips barely moves the needle and never triggers the draw at all. The zero power keeps the whole thing grounded: on a turn where you cast nothing expensive, this is a wall and nothing else, and every point of relevance has to be bought with mana that had somewhere else to be. Because the boost expires each turn, the clock resets and gets re-earned every time, so there is no snowballing threat to fear, only a body that turns your interaction and your big finishers into incidental damage while it refills your hand. It is built to sit behind a stack of costly noncreature spells and tax nothing you were not already paying: the mana was spent regardless, and the creature converts it into pressure and cards at once.