From publisher blurb:
The ancient heroes of lore succeeded in their quest to destroy the elemental titans that are primordial corruptions, but have inadvertently doomed the mortal realm to an apocalypse none has ever seen. With the cycle interrupted, the four elemental planes simultaneously swell and threaten to remake the world in their image. Meanwhile, the new primordial corruptions prepare to invade.
You'll find the following within this compendium's 33 pages:
3 pages of lore about the cycle of Primordial Awakenings and how they have changed, as well as ways to implement them into your game
64 options to differentiate your elemental rifts, from appearances to locations to regional effects
10 adventure hooks to kick off an elemental incursion campaign
1 elemental ranger subclass for shepherds of elemental spirits
20 elemental items, from void-made Null Reaver to four elemental weapons that combine into an artifact
4 sets of elemental corruption templates to grant monsters elemental flavor
9 elemental foes, including four massive CR 25-28 primordial corruptions to potentially destroy your world