"Hell Eggs" is the name given to several artifacts created by Dread Empress Triumphant and carried by her Legions of Terror. Most of these were destroyed in the First Crusade that toppled Triumphant, but a few still survive scattered throughout Calernia.
A Hell Egg is a Legion battle standard (actually just the staff, the flag is optional) to which is bound a Demon and an army of 100 Devils. A diabolist wielding the standard can deploy these fiends in battle and call them back into the standard afterward. Hell Eggs are even more dangerous weapons today than they were when they were created, because the devils in them are now all hundreds of years old and therefore much smarter than freshly-summoned ones.
Akua Sahelian the Heiress unleashed a Hell Egg containing a demon of Corruption on Marchford, assailing the city with fiends and also corrupted remnants of the Silver Spears mercenaries, causing a terrible battle that mauled Catherine's Fifteenth Legion. Another Hell Egg containing a demon of Absence was found and destroyed by heroes during the Tenth Crusade.