An Egg of Brimstone is a magical object which, if smashed, releases a flash and some smoke.
History
An Egg of Brimstone was present among the multiple magical objects in the Chamber of Crowe. Michael Clarke took one with him which he used on the Zarantulus to give him, Tom and Benny time to rescue Ursula Crowe. Dawn of the Nekross
When Warlock arrived in the Chamber of Crowe, Michael threw one at his feet to hold him off. This, however, was ineffective and Warlock then injured Michael. Twilight Falls
