Pulse stone

A pulse stone is a bluish, glowing, baseball-sized crystal able to attract undead in 30 feet radius. Those who fail DC 15 Wisdom saving throw, start to walk over to the gem and begin to stare at it.

History
A pulse stone rested in the center chamber of the large temple in Thomara city and surround by a number of zombies and skeletons attracte to the crystal. It was delivered to Vox Machina by Scanlan's invisible servant (named Simon 2) and was put into the Bag of Holding.

Percy attached the pulse stone to the infinite rope and threw it near the single entrance to the Tower of Entropis to distract the rot behemoth wathcing over it. When the party entered the tower, he pulled it back and threw it again in the center of the ground floor to distract undead wandering this chamber.