Sword of Power

It rewards the powerful with power and the meek with weakness.

A chunky great sword

(-4 to +20), (-4 to +20) great sword

Enchantment varies based on your current HP: It starts at -4, -4, and gains +1, +1 for every 5 HP up to 40, and then a further +1, +1 for every 10 HP beyond 40 up to 200.

Desirability

Although beefy characters, especially berserkers, can get satisfying results out of this, it prevents the use of a shield and becomes useless just when things look most grim. Don't use without some means of quick escape and a solid backup weapon. Alternatively, just use a well-enchanted, branded triple sword.