Definitely need a cost on the ability: "suffer 1 ft to refresh..." or "during your turn exhaust one of your skills to refresh..."
The Feat is a good idea, but there is some missing verbiage. I have a custom class skill that has this sort of mechanism and had to flush it out this way (use any of this verbiage you like):
"Place your hero token under its base to identify this monster" and, "The monster recovers half of its life total, rounded down" and, "The monster activates as a familiar and is treated as a hero figure" and (If you want to be able to use monster abilities), "You control all decisions and actions of this monster. All monster abilities referencing “hero” are replaced with “monster” and vice versa." This all becomes very instructive and falls victim to space-limitations on the hero sheet.
Also, I don't think you considered the implications of the ability/stat trade-offs. You may need him to roll a brown defense die and reduce his health to 10 (or 8 health and keep the gray die?) or reduce his Speed/Stamina equation given the powerful ability.