Going off the "reconstruction" concept, what if it randomly converted up to 3 points worth of hp/att each turn for the target creature.
Let's say, turn one, played on armagio. It goes from 1/25, to 2/24 (1 point swapped to attack, the remaining 2 points swapped back and forth). The next turn, it goes to 5/21 (converting 3 HP into attack), and on turn 3, it goes to 4/22, followed by 1/25 (totally random).
This way, the creature will randomly gain more health and attack, while losing the other. It doesn't gain any new stats, it just swaps out numbers.