I remember a time when men drew on purer sources, and communed with the ancient spirits around them. It was not power that they sought, but harmony, to become one with the world. They spoke with the wind, walked among the flames, moved in time with the earth and flowed with the drifting of the tides.
These men were better for it, stronger of heart and soul than those who greedily grasped at powers from the hells. Do you doubt me? Then let me show you...
These invocations are intended for use with the warlock class, to add a few more options in terms of mechanics and flavor. Fey, fiends, and other outsiders are all well and good, but I felt like the elementals were underrepresented. So, here are some totally not inspired by Avatar invocations.
Master of Earth and Stone
When you use this invocation, you gain mastery over earth and stone. For the duration of the invocation, you may use the following spells as spell-like abilities: excavate, fabricate, (creating stone, clay, and earthen items only) move earth, soften earth and stone, spike stones, stone shape, transmute mud to rock, transmute rock to mud, and wall of stone, except that they have an instantaneous duration if they do not already. In addition, while this invocation is active, you benefit from the earthen grace spell. This invocation lasts 24 hours.
One with Earth
When you use this invocation, you attune yourself to the earth. You gain a burrow speed equal to half your land speed, and can burrow through stone, dirt, and almost any sort of earthen material except metal. You may choose whether or not you leave a tunnel that others can pass through. In addition, you gain 15ft tremorsense. The duration of this invocation is 24 hours.
Least; 1st; Eldritch Essence
This eldritch essence invocation allows you to change your eldritch blast into a riverflow blast. A riverflow blast deals bludgeoning damage, and is affected by damage reduction, but ignores spell resistance. In addition, every use of riverflow blast creates 30 gallons of nonmagical fresh water.
Lesser; 4th; Eldritch Essence
This eldritch essence invocation allows you to change your eldritch blast into a sandstorm blast. A sandstorm blast deals piercing damage and is affected by damage reduction. Any living creature struck by sandstorm blast must make a fortitude save or take 1 constitution damage.
Least; 2nd; Eldritch Essence
This eldritch essence invocation allows you to change your eldritch blast into a searing blast. In addition to normal damage from eldritch blast, any target struck by a searing blast takes fire damage equal to your Charisma modifier, and must make a Fortitude save or be dazzled for 1 minute. If you desire, you may make all of your eldritch blast damage fire damage when you apply this eldritch essence.
Shield of the Depths
When you use this invocation, you create a thin field of water around yourself. This effect grants you a number of temporary hit points equal to your caster level. In addition, you regain a number of lost temporary hit points equal to 1/4th of your caster level every round (though you can never have a number of temporary hit points greater than your caster level). The duration of this invocation is 24 hours.
Sing the Winds
You call to the winds, and they answer. You may use control weather as the spell, except the weather you call need not be appropriate to the current season. Like the spell it mimics, Sing the Winds has a 10 minute casting time. The duration of this invocation is 24 hours.
Dark; 8th; Eldritch Essence
This eldritch essence invocation allows you to change your eldritch blast into a storm blast. A storm blast deals electric damage. Any creature struck by a storm blast must make a reflex save, or be paralyzed for one round. On the next round, any creature struck by a storm blast is dealt sonic damage equal to half the damage rolled for the storm blast, and must make a fortitude save or be deafened for 1 minute.
Once per round when you would normally be hit with a ranged weapon, you may deflect it so that you take no damage from it. You must be aware of the attack and not flat-footed. You may not deflect massive ranged weapons (such as attacks from siege weapons) or ranged attacks generated by spell effects. In addition, your flight speed increases by 10 feet, and your maneuverability improves by one step, to a maximum of perfect. You do not gain a flight speed if you do not have one. The duration of this invocation is 24 hours.
This invocation creates a floating flame that stays within 120 feet of you, staying at a position relative to you that you designate (you may change this position as a free action). The ward torch cannot pass through solid objects, and if the position you designate to it would force it into a solid object, it is immediately extinguished. The heat of the ward torch is no more than a candle and it cannot deal damage, but it sheds light as a torch. As a swift action, you may expend the ward torch to produce the effects of a pyrotechnics spell (with the ward torch being the required fire source). You are immune to the blinding effect if you use the fireworks version of pyrotechnics. You may have a number of ward torches active at one time equal to the number of invocation grades you know. A ward torch lasts 24 hours, or until expended.
Using this invocation creates a blast of air with a speed between 1mph and 75mph. This wind affects one of the following areas: a 60 foot line, a 30 foot cone, or a 15ft burst centered on you. You decide on the area when you use the invocation, and it emanates from you for one round. Wind Force has all the effects of a wind with the chosen speed within that area. The normal Fortitude saves to negate the effects of the wind are replaced by the save DC of the invocation. In addition, spell resistance applies against the wind's effects.
Work the Waters
This invocation grants you three spell-like abilities, which you may use at will. All of these abilities have a range of 400 feet, + 40 feet per caster level, and target 1 cubic foot of inanimate, unattended water per caster level. This invocation has a duration of 24 hours.
Move Water: As a move action, you can move water up to 50 feet in any direction. So long as this invocation is still active, and the water is in range, it remains where you have moved it.
Maneuver Water: As a standard action, you can control water to make a bull rush, disarm, grapple (including pin), or trip attempt against any target adjacent to at least one cubic foot of water. Resolve these attempts as normal, except that they donít provoke attacks of opportunity, you use your caster level in place of your base attack bonus (for disarm and grapple), you use your Charisma modifier in place of your Strength or Dexterity modifier, and a failed attempt doesnít allow a reactive attempt by the target (such as for disarm or trip). No save is allowed against these attempts, but spell resistance applies normally.
Manipulate Water: As a move action, you can change the general shape of water, though fine detail isn't possible. So long as this invocation is still active and the water is in range, it remains in the last shape you gave it.
Edit: Now version 1.1, with some edits made.