The Stone Ring
Trigger: Kill all of: 2 x A Crumbling Stone Mass", 2 x "A Rock Creation", 2 x "A Pile of Boulders", 2 x "A Boulder Thrower".
Phase One to Five: About 50 "A Stone Fortification" will spawn. These can be pulled in bunches and AE'd.
Phase Six: Four "A Mound of Rubble" will spawn. When low on health, these mobs become suddenly resume full hit points and disengage from combat, walking back to their platform. Be careful not to accidentally kill any. When the 4th one begins walking back, "A Rock Monstrosity" will spawn and immediately charge the raid.
Phase Seven: Kill "A Rock Monstrosity", but be ready for more fighting immediately. 4 "A Stone Heap" will spawn and immediately rush the raid.
Phases Eight to Twelve: Six waves of 4 "A Stone Heap" each will spawn and rush the raid, each wave spawning when the previous 4 are all dead. If you need a break to prepare for the boss mob, you need to set aside one "A Stone Heap" and mesmerize it.. When the final "A Stone Heap" dies, Peregrin Rockskull will charge the raid.
The Boss: Peregrin Rockskull hits for 2k and may memblur himself. He uses the Pebble Rain AE, which is an easily resisted MR-based snare/DD.
Loot: Peregrin Rockskull does not drop elemental molds/patterns, but does drop 2 other EP-quality loot each time.