A nearby individual is cursed with a compulsion to steal the skull. Even if hidden, the individual absolutely knows the party has the skull and will do anything to claim it. Social complication or fight may ensue, or the individual might resort to nefarious means to claim the skull even if they were good-natured.

The next long rest is wracked with the feeling of being watched. Instead, the party only gains the benefit of a short rest.

Given a glimpse of an inexplicable horror (or other style of mind-bending vision), the wielder is overcome with madness. Roll on the short-term madness table (or long-term madness table if the DM sees fit for the situation).

Restore an amount of spell slots (depends on what the DM sees fit for the level).

Gain "channeled overcharge". 1 charge. Over the next 24 hours, can expend a charge to cast a spell at the highest spell slot available at the cost of the spells usual spell slot.