The lantern was rectangular with a half-foot-by-half-foot base. It had two standard lantern shutters, one each on opposite sides. On a third side, it contained a vertical column of five knobs. One side of the lantern was lit, and its corresponding shutter functioned normally. The other side, however, contained a black, quivering membrane that was warm to the touch and rubbery. A metal plate divided the two sides of the lantern internally, but each of the five knobs could open a vent on the metal plate that would allow light from the one side to pass into the other side.
If the shutter on the side of the lantern with the dark membrane was opened and the lantern was lit, turning one of the knobs would allow the light to cross the metal barrier and animate the black membrane, which would become a tendril, stretching out of the open lantern. Turning more of the knobs would lengthen the tendril.
The tendril would attack opponents by lashing out like a whip. Being struck by the tendril would also cause paralyzation. The tendril would also seek to enwrap and constrict its prey.
The lantern's tendril was resistant to blunt weapons, because of its rubbery texture, but it could be damaged by blades and points. If the tendril was destroyed, a new one could only be created by a series of magical spells listed in the spellbook of the item's original creator.
The Tendrilight was the last magical item created by the Cowled Wizard Rashal of Amn. Rashal died shortly after the creation of this lantern, and it passed into the control of the other Cowled Wizards.
Later, the magic lantern was sold to a merchant company, and then it was sold or passed on many times before becoming the property of one of the members of the Order of the Blue Boar named Crosess Whitedove.
At Whitedove's death in the early 1300s DR, the lantern was inherited by a student of Crosess' named Helrik Redsash. Helrick vanished in the Snowflake Mountains while on an adventure, and the lantern is believed to rest there somewhere.