Gigantoplasm

Most clone creatures hand you a static copy and walk away: point Clone or Phantasmal Image at a body and you live and die at its printed stats. The wrinkle here is the bolt-on activated ability the copy keeps no matter what it copied. Snapshot a 7/7 beater, then set its base power and toughness to whatever X you can afford in the moment, and the clone stops being a fixed reflection and starts being a dial. Because the granted ability sets base power and toughness rather than adding to it, it overwrites the copied creature's natural size entirely, so the X you pay is floor and ceiling at once, recalculated every activation. That cuts in both directions, though carefully: copy a small utility creature for its ability and pump it into a finisher when spare mana shows up, or scale it back down on a later turn. The X=0 line is real but blunt: a 0/0 dies to state-based actions, so it is a one-time off switch (a way to end your own copy on your terms), not a repeatable sacrifice valve, and the death is to lethal toughness rather than to a sacrifice, so it answers to neither sacrifice triggers nor sacrifice-only payoffs. The card is less a clone than a programmable chassis: it borrows another creature's text but reserves the right to be any size it wants, which keeps it relevant long after the thing it copied would have been outclassed.