From publisher blurb:
Elementals Unleashed!
Mythic Monsters: Elementals brings you an awesome array of elemental enemies from every part of the planes of fundamental matter and energy. These amorphous adversaries range from CR 3 to CR 22, and include true elementals ranging from crackling lightning elementals to suffocating mud elementals and raging-hot magma elementals to deathly frozen ice elementals. There are elemental creates of silent and subtle lethality like the aerial servant and simple wanton pyromaniacal glee like the magmin. Skittering crysmals are as deadly sharp as they are beautiful, and beauty is only the beginning for the nymph-like veela of that inhabit the planes of earth, fire, and water. Like the veela, the manifold mephits are not true elementals but embody the essence of the elemental planes in a way almost familiar to the humanoids who summon them, though the denizens of the elemental planes can be wholly alien like the bizarre aquatic tojanida. Finally, the fierce scanderig forgefiend represents the taming of the power of the elements by craft and artifice, while the majestic anemos represents the power of wild wind and weather from the farthest corners of the world. As if that were not enough, we bring you new spells and feats to push the boundaries of elemental summoning, plus introduce the fission elemental template that shifts from a towering colossus to a seething swarm of raw elemental fury!