Amulet of Life and Death

Wondrous Item, very rare (requires attunement) Your Constitution score is 19 while you wear this amulet. It has no effect on you if your Constitution is 19 or higher without it. Once per long rest, if you clutch the amulet (as a bonus action) and whisper “life”, it will heal you of half your maximum hit points.
Once per long rest, if instead you clutch the amulet (as a bonus action) and whisper “death”, your next successful attack will damage your target for half your maximum hit points, but each time you do so you risk the amulet entering a permanent eclipse upon the successful attack.
A permanent eclipse will cause the amulet to take as many hit points from you as your maximum, and render the amulet a burned out shell.