I want to see interesting cursed items that people will want to use.
Wish granted!
Here's my campaign's take on Stormbringer:
Heartsbane
Heartsbane is a magical
greatsword +1 inhabited by a vengeful elemental spirit that demands a daily sacrifice of blood.
A creature may spend 1 hour performing a ritual to attune to Heartsbane. During the ritual the elemental spirit whispers to the creature performing the ritual and demands blood sacrifices for power.
An attuned creature gains access to the following ability and suffers from the drawback.
Life Drain: once per short rest after scoring a critical hit or a killing blow with
Heartsbane the wielder gains temporary hit points equal to half of the damage caused by the attack.
Drawback: if the creature attuned to
Heartsbane has not used the Life Drain power in the last 24 hours that person’s maximum hit points and current hit point total are reduced by 5 per hit die after a long rest. This reduction is not cumulative with itself and remains effective until the creature uses the Life Drain power. Using the Life Drain power does not restore current hit points, but removes the penalty to maximum hit points.
If the creature’s current hit point total falls to zero because of this drawback, the creature dies immediately (no death saves required).
If the creature’s maximum hit points falls to zero because of this drawback, the creature dies immediately (no death saves required), and it's soul is trapped by the spirit inhabiting
Heartsbane (as minimus containment version of the
Imprisonment spell).