Spoiler: The Sword of Tariel (improved)
In Theo's hands, this weapon now functions as a +2 Keen Holy Heavenly Burst Greatsword with permanently affixed Crystal of Greater Energy Assault (electricity)

It also allows use of the spell-like abilities below (as a cleric whose caster level equals Theo's character level and using Theo's stats):

At will: Detect Evil, Tongues
3/day: Mass Align Weapon, Protection from Evil, Lesser Restoration
1/day: Visage of the Deity