Before we start, i need to mention that this guide is based on MY PERSONAL experience, thoughts and feelings for Elementalist so it might not be 100% accurate, or you might not agree with me.

What is this class capable of? What can you do?

Pros :

• very versatile : he can teleport, become invulnerable, heal
  
• good fighting power : big AOEs, can attack from a safe distance, can nuke out the whole map in a few seconds, can burst a single big target fast

Cons :

• gets LITERALLY 1 shot (or 2 shot in the best case scenario, depends on the difficulty you are playing on)
  
• has a hard time against a group of big targets (like a group of 3 champions for example)
  
• has no chance beyond Inhuman Ordeal 2 (or at least i couldn't make him work)

I recommand investing your ability points in the following order :

• 1 Corporeal Balance
  
• 3 Elemental Mastery
  
• 3 Arcane Influence

Until you hit the cap for critical damage which is 450% and afterwards stop putting points into Arcane Influence and keep a 1:3 ratio with Corporeal Balance and Elemental Mastery. At some point you will get more and more critical damage from items, so you can remove a few points and spend them in Corporeal Balance and Elemental Mastery

The reason for doing so is because Elemental Mastery increases the damage of your spells and elemental resistance (spells of the mobs) while Corporeal Balance increases your HP and defense which gives you percentage damage reduction.

At lv 100 with the items i have right now (which are not the best atm), my stats looks like this :


Before saying "this class is trash, the dmg is so low" you have to keep in mind that the dmg of Stream of Bolts is what you see x9 and the damage of Icicle Swarm x5 and it can also crit.

In my opinion these are the skills you need and also the order of getting them

Basic skills :

• Energy Bolt (10 points)
  
• Icicle Swarm (10 points)
  
• Stream of Bolts (10 points)

Intermediate skills :

• Ray of Frost (5 points) - please don't use this skill
  
• Ray of Entropy (5 points) - please don't use this skill
  
• Ray of Destruction (at least 1 point)
  
• Fire Wall (5 points) - please don't use this skill
  
• Frost Barrier (5 points)
  
• Blazing Barrier (at least 1 point)
  
• Mirror Image (5 points)
  
• Painlessness (at least 1 point)
  
• Ink Leap (at least 1 point)

The reason i said "please don't use this skill" is because the skill itself is bad/useless and you only need to invest 5 points in it so you can unlock the next tier skill.

Advanced Skills :

• Ray of Destruction (10 points)
  
• Blazing Barrier (10 points)
  
• Frost Barrier (10 points)
  
• Painlessness (10 points)
  
• Mirror Image (10 points)
  
• Ink Leap (10 points)

Basic Powerups and Masteries

• Ray of Destruction
  - Deathburst (Powerup) [GET THIS AS FAST AS POSSIBLE]
  
• Energy Bolt
  - Channeled Bolts (Powerup)
  
• Icicle Swarm
  - Greater Swarm (Mastery)
  - Greater Swarm (Powerup)
  
• Stream of Bolts
  - Swarm Bolts 3/3 (Mastery)
  
• Painlessness
  - Arcane Resilience (Mastery)
  
• Mirror Image
  - Simulracum Afinity (Mastery)

Intermediate Powerups and Masteries

• Ray of Destruction
  - Ray of Annihilation 3/3 (Mastery)
  - Ray of Death 3/3 (Mastery)
  
• Blazing Barrier
  - Fiery Sustenance 3/3 (Mastery)
  - Charring Flames 3/3 (Mastery)
  - Everlasting Flames 3/3 (Mastery)
  
• Frost Barrier
  - Eternal Cold (Mastery)
  - Cold Shock (Mastery)
  
• Ink Leap
  - Unyielding Soul 3/3 (Mastery)
  - Unburdened Soul 3/3 (Mastery)
  - Unfettered Soul 3/3 (Mastery)
  - Soul Echoes (Powerup)
  - Unrestrained Soul 3/3 (Mastery)
  
• Painlessness
  - Fearlessness (Mastery)
  
• Mirror Image
  - Improved Simulracum (Mastery)
  
• Stream of Bolts
  - Supercharged Bolts 3/3 (Mastery)
  - Spark Blast 3/3 (Mastery)
  - Enervating Bolts 3/3 (Mastery)
  
• Icicle Swarm
  - Freezing Icicles (Mastery)
  
• Energy Bolt
  - Surge Blast (Mastery)

Advanced Powerups and Masteries (situational / semi-useless)

[At this point you should have extra skill points]
[Also these are not in order of importance like the ones above, it's up to you the order you get them]

• Energy Bolt
  - Bolt Swarm (Powerup)
  - Shocking Bolts (Powerup)
  
• Icicle Swarm
  - Jagged Icicles (Powerup)
  - Freezing Icicles (Mastery)
  
• Stream of Bolts
  - Raw Force (Powerup)
  
• Ray of Destruction
  - Ray of Devastation (Powerup)
  - Draining Ray (Powerup)
  
• Blazing Barrier
  - Infernal Barrier (Powerup)
  - Hellspawn (Powerup)
  
• Frost Barrier
  - Soul Chill (Powerup)
  - Frost Statues (Powerup)
  
• Mirror Image
  - Fortified Illusion (Powerup)
  - Deadly Illusion (Powerup)
  - Lasting Illusion (Powerup)
  
• Painlessness
  - Regeneration (Powerup)

Why don't you max Ray of Frost and Ray of Entropy to increase your Ray of Destruction Damage?
Well, Ray of Destruction is one of your best skills, if not the best, but is not your main source of damage, you use it in a certain way. We will get to that later.

This is pretty straighforward and simple :

• Focus Damage (10 points)
  - Arcane (Mastery)
  
• Max Mana (10 points)
  - Cooldown (Mastery)
  
• Arcane Flux (10 points)
  - Arcane Meditation (Mastery)
  - Arcane Draining (Mastery)

In my opinion you should max your auras somewhere between after finishing your basic skills and finishing your intermediate skills.

Also another situational aura specially for late game, since your mana is not gonna be a problem anymore, would be :

Chaos Armor (10 points)
- Controlled Chaos (Mastery)
- Lasting Armor (Mastery)

For Katarina i use ranged form and for her behavior defend. Personally i think you can build Katarina's stats in 2 different ways :

• a bit tanky (less dmg)
  
• full DPS (dies a lot faster)

For tank Katarina build you should invest her ability points in the following order

• 1 Corpus
  
• 3 Kinesis
  
• 1 Ethereality

At lv 60 (which is max for her) her stats (with the items she has right now) looks like this :
(The screenshots are made on Inhuman Ordeal 2 so no... Katarina will not have these stats, but actually a lot lower depending on the difficulty your are playing on)



As for her skills, she looks like this :





For DPS Katarina build you should invest her ability points in the following order

• 1 Corpus
  
• 5 Kinesis
  
• 1 Ethereality

At lv 60 (which is max for her) her stats (with the items she has right now) looks like this :



As for her skills, she looks like this :





How to decide which Katarina build to use? Well i used tank Katarina until i had enough skills so i can deal/escape with/from mobs and afterwards i switched to DPS Katarina. So.. Until lv 80 tank Katarina, after lv 80 DPS Katarina.

Considering you can change these at any given time and it's cheap aswell, i will mention only the final 15 perks i'm using (i don't think i have all the perks so if there are better ones out there maybe i don't have them unlocked)

• Destructive
  
• Destructive II
  
• Devastator
  
• Elementalist
  
• Enlightened
  
• Focused
  
• Focused II
  
• Ghost Shepherd
  
• Ghost Whisperer
  
• Hunter Wizard
  
• Manifest Fury
  
• Marksman
  
• Marksman II
  
• Scholarly Ghost
  
• Wraith

Early game you should focus on getting ability points and skill points for you and Katarina.

What items should you use?
Well... Anything that increases your damage since you're a glasscannon class.

What bonuses should you add on your gear?

• % Bonus to All Damage (increases your damage, both for spells and weapon)
  
• Elemental Mastery (increases your Elemental Mastery stat so basically increases your damage with spells)
  
• Weapon Damage (increases your weapon damage)
  
• Arcane Influence (increases your mana)
  
• All Resistances
  
• Item Defense
  
• Physical Resistance
  
• Elemental Resistance
  
• Fire Damage Bonus
  
• Lightning Damage Bonus

What type of resistance to choose is based on your stats so if your Defense is low, go for Item Defense, if your Physical Resistance is low go for that... you get the idea.

Why Fire Damage and Lightning Damage?

Well a lot of your skills are lightning. Energy Bolt, Stream Bolts, Ray of Destruction (this skill has all types) so increasing your Lightning Damage boosts the damage of 3 skills at the same time.

About Fire Damage huh? Well the damage from your Blazing Barrier is actually underrated first of all. Second to that you use Frost Barrier and Blazing Barrier together on enemies who are far away from you to stall time with the freezing/slow effect and damage them before they get to you right? Hey, it's free damage, who says no to that? Since Frost Barrier's damage is not very high your damage comes from Blazing Barrier so you should increase it if you get the opportunity. Also Ice Damage would help only your Icicle Swarm and since that ability is already your second biggest DPS ability you have i don't see the point.

IDEAL ITEMS :

Getting all these items will be either very hard or close to impossible but in my opinion these are the best items in the best combination possible (fully enchanted of course).

Van Helsing :

Immaculatus Weapon , Amulet , Armor , Cloak
Conjurer Mask, Gauntlets
Manticore Belt, Boots, Trophy
Spirit Runic Ring x2

Katarina :

Crimson Terror Wraith Claw , Amulet , Wraith Cloak , Wraith Mark
Arcane Prodigy Ring x2

The most important thing is kiting. If you don't kite you will die.
What's kiting?
Using an attack/ability then move back slightly, using another attack/ability then move back slightly again and so on. Basically kiting means attacking and running away from your target at the same time.

Combos :

Step 1. Use your Frost Barrier (freezes and slows enemies and also lasts longer than Blazing Barrier)
Step 2. Use your Blazing Barrier
Step 3. Summon your Mirror Image

Now that you have drawn the "path of pain" for mobs you also get 2 bodyguards to defend you from mobs. Normally your Mirror Image should take aggro first so Katarina will have some time to deal damage before she takes aggro too. If there are a lot of enemies she will take aggro aswell which is a good thing, that's what you want from her... to tank the damage instead of you. Unless he dies to a mob, your clone will have lower cooldown than the duration of the skill, but when you summon the second clone, the first one will disappear.

Step 4. Use your Stream of Bolts until you deplenish your extra energy bolts around you. (when you have all 6 of your extra energy bolts around you, this skill has the highest DPS)
Step 5. Use your Icicle Swarm
Step 6. Use your Energy Bolt while your Icicle Swarm is on cooldown
Step 7. Use your Icicle Swarm again now that it's off cooldown
Step 8. Use your Stream of Bolts again since you should have some extra energy bolts again
Step 9. Go back to step 1

What about Ray of Destruction? You said it's one of your best skills.
I'm glad you asked :D You do all these steps i wrote above to prepare your best weapon, and their biggest nightmare : THE NUKE ! Once you have a group of mobs stacking up together or at least 1 low hp mob, all you have to do is activate your Painlessness, use your rage to empower your powerup 3 times and blast them away to another dimension with Ray of Destruction. Basically when you kill a mob this way, he explodes for 150% damage of his MAX HP and this skill can also crit PogChamp!!! That means an additional 450% damage. And normally after you kill 1 mob this way, not only that a lot more should die at the same time, but other mobs will become low HP and a chain of nuking will start :D This helps you out in 2 different ways :
1. you clear the map fast
2. it's the fastest method to kill a very big hp mob, by exploding the smaller mobs around him, since a lot of time mobs will explode from 200k to 4 millions... it all depends on their hp and the way you line things up.

Mobs that you will get to hate :

• poison mobs (they appear on all stages of the game)
  
• the classic group of 3 champions who's health bar is bigger than you can count
  
• mobs who teleport (to you or far away from you)
  
• mobs who pull you
  
• mobs who cc you (like freezing)

This was my guide, i think it covers all you need to know about this class and i hope you liked it, and if you did please don't forget to rate it aswell, especially since it's my first guide :)