Menhir Circle

It claims a debt and offers a loan.
Benefit: When you attune to this item, your maximum HP is reduced by 10 HP plus 3 HP per character level you possess, and one other willing ally that is within [Medium] range has its maximum HP increased by 20 HP + 6 HP per character level they possess. This effect lasts until you are no longer attuned to this item. If your ally dies or ceases to be considered an ally for this effect, you become unattuned from the Menhir Circle and the effect ends. A creature may only have its maximum HP increased by one Menhir Circle at a time.