Oculus of Abaddon

This artifact doubles the duration of all spells cast by its wearer as though using the Extend Spell feat. Three times per day its wearer can peer into it to cast true seeing spell as a 20th level wizard. Yet, staring into this gem is dangerous: whenever the wearer uses this ability, they must succeed on a Wisdom check (DC 15), to avoid seeing something truly unsettling... Or worse – be seen by it.