So, I always liked the idea behind the Elemental Warrior Prestige Class from the D&D Planar Handbook. A fighter getting in touch wtih one of the elementsm gaining some measure of control over it, and incorporating it into their combat style just has so much cool potential. A fighter who can make their sword burst into flames, or melt anything they stab just sounds awesome.
So I've reworked the Elemental Warrior into a Fighter Archetype. The biggest change is probably giving the character a way to change what element they have an affinity to. I wanted to avoid the situation of an Elemental Warrior being doomed to uselessness if the party went up against anything with resistance to their Element, but I kept the realignment time long enough that you can't just change your element on the fly.
Needless to say, I've got no idea how balanced this is, if at all. I'm also open to any alternate ideas of how to make the concept work.
Align Element: At the start of each day, an Elemental Warrior must spend one minute meditating upon one of the four elements (air, earth, fire, and water) in order to align themselves with that Element. An Elemental Warrior may change their aligned element at any time by spending five minutes in meditation. Changing your aligned element does not refresh uses of Elemental Weapon or Elemental Manifestation.
Resistance: At 2nd level, an Elemental Warrior gains energy resistance 5 against their current aligned element, and a +1 bonus on any saying throws against spells, spell-like abilities or supernatural abilities which inflict that type of Elemental damage. The energy resistance increases by 5 points and the bonus to saving throws increases by +1 for every four levels beyond 2nd.
This ability replaces bravery.
Elemental Weapon: At 3rd level, as part of making an attck action an Elemental Warrior may choose to deal an additional 1d6 damage of a type matching their aligned element. You must declare that you are using this ability before rolling to hit (on a missed attack, it is wasted) The Elemental Warrior may use Elemental Strike number of times per day equal to their class level + their Wisdom Modifier.
At 7th level, and four levels thereafter, the amount of elemental damage inflicted by Elemental Strike increases by 1d6.
This ability replaces Weapon Training 1, 2, 3, and 4.
Elemental Manifestation: At 5th level, the Elemental Warrior gains the ability to manifest an aspect of their aligned element. Elemental Manifestation may be activated as a swift action, and used for a number of rounds per day equal to the Elemantal Warrior's level + their Wis mod.
Air: Brisk winds whip around the elemental warrior’s body. All ranged attacks against them have a 20% miss chance. For every four additional levels of Elemental Warrior, the miss chance increases by 10%.
Earth: The elemental warrior’s skin is partially sheathed in rocky hide. Their natural armor bonus increases by 2. For every four additional levels of Elemental Warrior, the Elemental Warrior's natural armor bonus increases by 1.
Fire: A sheath of flame envelops the elemental warrior. Anyone adjacent to the Elemental Warrior takes 2d6 fire damage. For every four additional levels of Elemental Warrior, the fire damage increases by 1d6.
Water: The elemental warrior body becomes liquid and flowing, able to bend and dodge in seemingly impossible ways. All melee attacks against them have a 20% miss chance. For every four additional levels of Elemental Warrior, the miss chance increases by 10%.
This ability replaces Weapon training 1, 2, and 4.
Elemental Strike: At 13th level, the Elemental Warrior's Elemental Strike gains one of the following effects, depending upon their aligned element The enemy may attempt a fortitude save to negate this effect (DC 10 + 1/2 the Elemental Warrior's level + the Elemental Warrior's Wis modifier).
Air: The target is knocked prone.
Earth: The target is entangled for one round.
Fire: The target is shaken for one round.
Water: The target is sickened for one round.
This ability replaces Weapon Training 3.
Elemental Mastery: The Elemental Warrior gains complete immunity to damage caused by their aligned element. In additon, the Elemental Warrior's mastery of their abilities is such that once per day an Elemental Warrior may change their aligned element as a full-round action.
This ability replaces Armor Mastery.
Dual Alignment: The Elemental Warrior may be aligned with two different elements simultaneously, giving them complete immunity to two types of energy damage, granting two different effects for Elemental manifestation, and effectively doubling the damage provided by Elemental Weapon.
This ability replaces Weapon Mastery.
I like the spirit of what you wrote, but I think you are holding back. This could be better.
Instead of using the fighter as a base, why don't you use the Paladin as a base? You could justify WAY stronger abilities in exchange for Lay on Hands, Spell Casting, Animal Companion, and Smite Evil. In the end, it is the abilities that make this class.
That is a very good idea.