Molder

The X scales two ways at once, and that is the whole reason this answer reads differently from the green disenchant spells that share its job. Pay one green and as much extra as you like, and the spell destroys an artifact or enchantment whose mana value matches X exactly: not "X or less," not "any," but a tuned key cut for a single lock. The lifegain rides the same number, so a big payment for a big permanent refunds a chunk of the cost in life. The exact-match clause is what makes the design unusual. It refuses to be a cheap catch-all; you have to know precisely what you are pointing it at and size the cast to fit, since you cannot even put it on the stack without a legal target whose mana value equals the X you announced. Green has always answered artifacts and enchantments at instant speed (Naturalize and its many cousins set the baseline), but those pay a flat rate regardless of the target. Tying both the destruction and the life swing to a precise value turns a utility removal slot into a measuring instrument: the cost tells you exactly what you decided to break, and the life total tells you how much it was worth. The "can't be regenerated" rider matters less now than it did when regeneration was a live concern, but it signals intent: a clean, final answer rather than a tempo trade.