|You must be turned into a Spriggan and have the 'Transfiguration' buff on you. Talking with the nearby Sylphic Sorceress will enable you to be transfigured. Attack the Enormous Egg with your new ability, 'Quickchant', and stand safe zone of the Egg's attack. The Egg does a 270 degree (centered around itself) attack, with a moving 90 degree safe spot. Just stand in the safe spot and spam Quickchant to win. At 70% and 35% health, several spriggan golems will appear and may knock you back. Just take care to not be knocked back into the AOE and you'll scramble the egg!
The egg's health varies depending on how many people were engaged in combat with it the previous time it was killed. The number of shots of Quickchant it takes to defeat it can vary from 62 to 115 shots or more.