Mind into Matter

X is spent once but gates two effects, and the second gate is what makes the card sing: draw X cards, then that same X becomes the mana-value ceiling on whatever permanent you drop for free. The two halves pull against each other on purpose. A small X refills cheaply but caps you at a mana rock or a two-drop; a large X finds the bomb and pays its own mass, but you have already tapped out the resources you would want back. The ceiling is a maximum, not a minimum: draw seven and anything of mana value seven or less is fair game, from a Sol Ring you happened to draw up to the biggest permanent in the pile, so the number you chose gates the top end and leaves everything beneath it open. The permanent arrives tapped, which is the restriction keeping this from being a green-blue Sneak Attack at sorcery speed: a fresh creature cannot swing or block until it untaps, and a would-be haste finisher stalls a full rotation before it does anything. Functionally it is a self-selecting tutor that draws into its own answer, buying a chunk of cards and dropping, in the same resolution, the largest permanent that chunk can support without paying its cost. Every decision is front-loaded into a single number, so by the time the draw resolves you already know exactly how large your free reward is allowed to be.