It seems that I need to generate a pdf for all the primordials posts. With that in mind, I'll briefly mention earth and air primordials before moving on to different types.
The earth and air primordials share an ability to become incorporeal. The earth primordial uses this ability to move through solid earth. The air primordial lives as an incorporeal creature taking solid form only when feeding.
Incorporeal beings should not need to eat solid food. The Earth Primordial eats magic, specifically sucking the +3 off a sword +3. They are also magic resistant, a successful roll indicates that they consumed the spell hurled at them gaining a number of hit points or Constitution from it. Regardless of spell level or effect, an earth primordial receives 1d4 hit points from each magic item drained. There is no upper limit of hit points, after doubling its beginning hit dice, it will simply grow larger.
For GMs that stat monsters, they gain Constitution when feeding and lose it at the rate of one point a week. All spells provide a single point increase to their CON score. In the same way, regardless of plus, an earth primordial gains a single CON point by completely removing the magical effects from a magical weapon.
Yes, it would be an epic encounter if/when an earth primordial gains an artifact. The earth primordial would never drain an artifact, but will be provided an endless supply of food and a super-high CON score/hit points.
The land where Earth Primordials dwell features large landmasses broken up by small oceans. Much of the land resembles the Russian taiga complete with a rich diversity of wildlife and sentient races.
In their home plane, the Earth Primordials are scavengers constantly hunting for magic, usually left behind by unsuspecting travelers. Earth Primordials prefer the rich magicks available on the Prime Material Plane, but are seldom summoned. To get by on their home plane, many of compelled to travel to higher elevations. It seems that trees and other plant life are able to draw magic from the plane itself. It takes several fruit/acorns/pints from these plants to sustain an Earth Primordial, but there is just enough to keep the population alive.
Air primordials can feed from any corporeal creature draining a point of CON to sustain themselves. They enjoy a pastoral culture preferring to keep livestock to sustain themselves. Unless starving, an air primordial prefers to take one or two CON points at a feeding waiting for the CON damage to heal before feeding again. Since they require the equivalent of 4 points of Constitution a day, the herds of livestock normally number from 12 to 20 animals of various types.
Air Primordials practice a form of magic that promotes healing, divination and indirect attacks. (For GMs, consider them Clerics using the Priest's spell list.) They can also sacrifice a point of their own Constitution to heal other creatures once per day.
The plane of Air Primordials is filled will countless floating islands swirling in a multi-colored sky. The clarity of the atmosphere varying according to the season as well as the color of the sky. Air Primordials keep their herds these floating islands.
Culturally, the Air Primordials are not concerned with possessions as they have no real need for material things. They do not build houses or other structures. They lead an aesthetic life filled with contemplation. They have no enemies on the Primordial Plane of Air as they only the only sentient species there. There are other forms of the Air Primordials that are encountered, but all share the same characteristics. Humans on the Prime Material Plane call these other forms Fog Primordial and Smoke Primordial. Aside from a slight change in color in corporeal form, there is no statistical difference.
So, there's Earth and Air. Next time, I hope to really do something that is not Ptolemaic or Wu Xing.