Life Siphon

From BoardGameGeek:

Dragons have taken over the surface, forcing humans underground. During explorations, you and your fellow humans discover a box with an orange glowing eye on the outside. The words DO NOT OPEN are carved on the sides. Of course you open it...ONLY TO BE INSTANTLY CURSED! The only escape is to take out your closest friend with your new cursed powers to summon Familiars and cast spells at the cost of your own life. Each player's goal in Life Siphon is to defeat the player to their left, and the game ends when the first player drops to zero health, meaning you must plan your strategy to be effective offensively against one player while defending against another. Since everything costs your own health, the heavier your offense, the more vulnerable you are. You may even find yourself aiding your attacker to give you the opportunity to make the killing blow.