Technically, a warlock is a male witch (I think...there are so many contradictory opinions on what the word means, but Websters says it is essentially a masculine version of witch, so there you have it). This, however, is sort of influenced by the Palladium FRPG (imagine that), in that instead of deriving power from infernal means, the warlock draws his power from an elemental plane. The Elemental Control power could be easily abused, but a good DM should be able to come up with plenty of ways to keep it in check. These guys also have an alien mindset, and at higher levels probably don't even understand human emotion anymore. That might actually be a real roleplaying challenge.
Requirements: INT 12, WIS 15
Prime Requisite: INT, WIS
Hit Dice: 1d4
Maximum Level: None
XP Chart: Magic-User
Warlocks are similar to witches in that they make pacts with external sources to derive their power. Unlike witches, however, warlocks are more than simply a conduit for a demon or devil to act; they instead form a symbiotic relationship with an elemental plane, drawing energy directly from it. They cannot wear armor, and only employ small weapons like Magic-Users, who they fight as.
The Pact: Warlocks must pick a source of power, i.e. an elemental plane, and derive all their powers from this source. The DM is the final authority on what planes exist, but typically these include Fire, Water, Earth, Air, Energy (Positive or Negative) and Shadow. Para or Quasi elemental planes might also be available. This pact is not one of servitude; it is a voluntary relationship, almost parasitic in nature. Warlocks can be seen as a type of elemental priest, similar to Druids but far more limited in scope.
Elemental Nature: Warlocks see themselves as their patron element in humanoid form, and this influences their thinking and approach. Fire warlocks, for instance, are usually impulsive, almost psychotic at times. Earth warlocks would be more stoic and slow to act. Other elemental types can easily be extrapolated. At 5th Level spells affect them as if they were elementals; they are inhibited by spells such as Protection From Evil, but immune to Charm Person, for example. At 7th Level, a Warlock becomes totally immune to detrimental effects of his patron element. At 9th level, his body is no longer flesh and instead an expression of his element. He can only be harmed by magic weapons and magic and can freely switch between humanoid form and an elemental form of comparable HD (a 13th level Warlock can become a 13 HD elemental at will). At 11th Level, a Warlock can freely visit his elemental plane at will.
Summon Elemental: Warlocks can summon elementals, of any type, 1/day as per the spell. The elemental will be 1HD in size per level of the Warlock. Elementals from the Warlock's plane of influence will be 2HD in size/level. It will serve without question for 1 turn per level of the warlock (or until released), requiring no mental control. Warlocks will ALWAYS try to release elementals before they are destroyed. Any warlock who willingly causes the destruction of an elemental loses this power until he atones. Elementals are usually willing to risk their lives for Warlocks if the circumstances require it, and this isn't seen as a misuse of power. At 7th level, this power can be used 2/day, and at 11th level 3/day.
Elemental Control: Warlocks can control their element to some degree, increasing in ability as they increase in level. A warlock can generally affect his element in the same capacity as a Magic-User of the same level. For example, at 1st level, a fire warlock can create simple "fire bolts" (resembling magic missiles, possibly doing 1d3 damage), light small fires, create an effect similar to faerie fire, etc. At 3rd level, he would be able to simulate a Pyrotechnics spell or Resist fire. At 9th level, Wall of Fire or Flame Strike are possibilities, while at 17th level a Warlock has total control over his element. The player should determine the effect they wish to product, with the DM deciding if it is appropriate. This ability is NOT magical in nature, and is unaffected by anti-magic shells, dispel magic, etc. If used in combat, this ability takes 1 round of preparation per use (i.e. it can only be used every other round).
Magic Items: Warlocks have difficulty using magic items due to their elemental nature. At 1st level, they may use any item that is available to all character classes. At 5th level they are only able to use magic items related to their element or usable by elementals. At 9th level, warlocks can only employ items usable by elementals, and generally shun magic all-together, instead relying on their inherent powers.
Warlocks never gain followers, and no longer consider themselves human at higher levels. It is suspected that extremely powerful elemental lords were in fact warlocks at some point.