Maybe make it the same way the moves Psywave and Magnitude works?
Something like:
Probability.....% of HP Recovered
5%.....................0%HP
20%..................25%HP
50%..................50%HP
20%..................75%HP
5%...................100%HP
This makes it a high-risk/high-reward kind of move. Could be gamebreaking, or a waste of moveslot depending on player's luck. But then again, this might nerf the move too much. Thoughts?