You Compleat Me

Getting compleated is, in the fiction, an act of surrender, and here the mechanics honor that: your life total drops to 10 if it's higher and stays capped there permanently, and no removal will ever reach the emblem you receive in exchange. What the ceiling buys is a private engine welded to that life total: two life for any color of mana whenever you want it, plus a card every one of your upkeeps that costs one life. Both halves of the emblem spend the same resource the sorcery just fenced in, and that is the whole bargain. Ten stops being an abstraction when you are draining two here and bleeding one on every one of your turns there; the cap that reads as flavor is the meter that stops the engine from running unchecked. It looks like a downside spell and plays like a Phyrexian mana source you commit to before knowing whether you will survive long enough to profit. That is the design conceit running through the whole lineage of cards that address you in the second person and narrate a transformation as they resolve: the flavor of giving yourself over does the actual mechanical labor, and the emblem is made permanent precisely so the contract can never be torn up once signed.