Elementalist is a dual class of the sorcerer, it focuses on spirit skills & buffs. Like a lvl 15+ sorcerer, an elementalist can still only summon 2 spirits at once. The combinations of course being Fire & Wind, Earth & Water. 

To start im going to say Elementalists are not an easy choice, however they are a very fun class to play. If your looking for an easy to play char go spec instead. I’m going to get the con’s out of the way first, weed out the weak lol. 

Cons 

Lowest hp of all dual classes 
2nd weakest weapons in game (cleric wands are weaker still) 
Low evasion, critical rate, attack speed & hit rate (all magic classes have bad natural hr tho) 
Low Hp & Mp regeneration. 
Low spirit attack speed 

Pros 

Spirits. 
Very high mana pool 
Fast refreshing stun & debuff. 
Abililty to keep fighting even when your stunned. 
Very high damage potential in PvP

Stat Points 

The numbers for intelligence, constitution & strength may be correct, however beware dexterity has no effect on any form of evasion. Dexterity adds to your critical rate & deadly rate. 

For an elementalist; 

Intelligence will raise magic attack power and the attack power of spirits. 
Dexterity will raise your crit & deadly hit rate. I have not noticed any effect on spirit crit/deadly. 
Constitution will of course raise your health & mana. Again no effect noticed on spirit health. 
Strength will have no beneficial effect for elementalists or magic classes in general other then reducing weight.

Skills will require 100 intelligence, 17 dexterity & 17 constitution. 

Summary of skills. 

Active Skills 
For SP & level requirements see http://lastchaosinfo.wetpaint.com/page/Elementalist+general+skills 

ALL elementalists skills are vital to the class besides; 
Spirit blood (lv 38 )- This skill is broken and currently has zero effect. (note spirit haste does not increase attack speed as described but increases attack power) 
Soul of Fire (lv 32)- This skill is very weak, misses in pvp & kills the spirit. 
Sword of Wind (lv 38 )- While this skill is fine, the fire spirit’s skill lets this spirit combination down. 

Passive Skills 
For SP & level requirements see http://lastchaosinfo.wetpaint.com/page/Elementalist+passive+skills 

ALL elementalists passives are important. There are no passives you can miss to save SP. 

Helpful Advice 

Armour 
At low levels a pet on physical defence will help make up for non-upgraded armour. At higher levels I strongly recommend getting a pet on hp increase, as in pvp an elementalist’s low hp is his biggest disadvantage. b6 amour seals such as anti-stun/stone, speed-up have no effect on spirits. Casting-up appears to be bugged on spirit skills & i would not recommend wearing one. 

Level 77+ you should try get a full set of Evasion armour. 

See http://lastchaosinfo.wetpaint.com/page/75-137+armor+seals for more info on lv 77+ armour seals. 

Weapons 
Thanks to the introduction of Collecter Ryl, all weapons level 29-69 can be changed for a reasonable fee. Lv 73+ weapons will be a challenge as the elementalist population is grim at best. However that means elementalist weapons will be cheap most of the time. 

For 73+ weapons you should be aiming for a 5 blue sealed weapon, or a 5 green sealed weapon. 

See http://lastchaosinfo.wetpaint.com/page/73-133+weapon+seals for more info on lv 73+ weapon seals. 

Accesories 
For low levels i would recommend Rage of Demons to increase your magic atk & mana pool. 
At higher levels you will need monster combo accesories with Critical rate for grinding & Hit rate for PvP. If you can get hit rate accesories with evasion that is even better. 

Spirits 
Vital conversion is much faster then re-summoning a new pair of spirits. You have 2 vital conversions that can be alternated constantly untill the spirit is healed. 

If both your spirits are hurt badly, unequiping your weapon will kill them ready to resummon. 

Agro mobs can be tricky, just be mindful of where they are and where they respawn put your spirits on hold or protect while you lure some away from the pack. After lv 70 you should have mana screen which cuts down the damage spirits take considerably however keep an eye on your mana as it can empty very quickly if your spirits take too much heat. 

This is incorrect, the only thing that will affect spirits is spirit haste, weapon +’s & intelligence. 

PvP 
This is very simple really. Avoid the pointy things. 

Little hint for pvp, set your spirits to double attack. Use icespike on your desired target, however move before the animation starts. This will cancel the skill but your spirits will now have that person as a target. Makes for a much more precise option compared to using attack first. 

Use the above technique against warmaster run until jail of water lands, once they are stunned hit them with chain lightning, ancient weapon & icespike2. Icespike2 will slow them down enough for the water spirit to land a 2nd JoW hit them with more skills. Repeat until their hp is gone.  If you try to fight a warmaster head on you will not win. They have easily double your hp and a long stun. 

Royal knights below lvl 98 have a dash that can be cured using a basic cure. They will almost always dash in first as they dash hit them with jail of water & cure the stun then follow more or less the same technique as warmasters. 

Assassins are more or less the same as royal knights watch the snare instead. Spirits will follow invisible rogues & if you use jail of water on and invis rogue it will land making them stunned and visible. Also spirits will ignore assassin’s death motion and keep attacking. 

Ranged chars (demon form specs, rangers, archers & mages) are a little more difficult, hit them with chain lightning & ancient weapon with JoW and hand of earth. Keep using JoW as soon as it refreshes. 

This is all I can think of atm any comments or advice is welcome. 

Hopefully this provides a little more up to date info on a great class.  

Credits go to keithy008.