Okay guys, this is my first guide, i hope you enjoy this.
I think is very good this build, he make you really tank and you deal so much damage.

Pros + Extremely resistant + Good AOE damage (Area of effect) + You are a killer + Good chase with Thundering Smash + Ghost + Can escape a bit with rolling thunder or ghost

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Cons - Long Cooldowns - Early game you need a partner to got kills - You need time for the passive be usefull - Low health/damage early game - A % of HP damage can beat you easy

With this you make more damage, and resist so much.

• greater quintessence of desolation: Thundering Smash and Frenzy are Physical Damage, so with armor penetration you gonna do more damage.
  
• Greater Mark of Attack Speed: Because the additional AS in early game is so
  good with Frenzy
  
• Greater Seal of Armor: Is a good armor bonus in all the game
  
• Greater Glyph of Magic Resist: Is a good magic resist bonus in all the game

Heal: Make you safe while your passive is on.

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Ghost: Is nice to chase or escape with Thundering Smash

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Flash: If you dont like Ghost, you can pick this.

• Chosen of the storm: Mundo Ult like a passive.
  
• Rolling Thunder (Q): Singed Fling, but better.
  
• Frenzy (W): Your best ability, does alot of damage if you have so much HP.
  
• Majestic Roar (E): Your roar scares creeps and slow for long time.
  
• Thunder Claws (R): Your basic attacks deals so much damage, approximately the double.

• : That AS is awesome, with Frenzy you attack so much fast, and if you have so much damage + Stormbringer you rape so easy your enemies.
  
  
• : Best item of Volibear, more HP is more resist, and more damage with Frenzy . If you see a Volibear without this item, he sucks.
  
  
• : More HP, a good amount of damage, and slow with basic attacks. With this if you grab an enemy with Thundering Smash, probably he can't escape.
  
  
• : Give you Armor, and gain Attack Damage equal to 2% of your maximum Health. With 4000 HP, the 2% of this is 80, so you gain 80 damage.
  
  
• : Gives you so much magic resist, movement speed and more Health Regen, with The Relentless Storm and Warmog's Armor you regen so much per second.
  
  
• : You are very tank, if you die and your teammates cover you while you revive, you dont die.

Farming:

You should start farming to buy Giant's Belt or to gain more HP with Warmog's Armor

Jungling:

You shouldn't jungle with Volibear, but if you gonna do it look this.

The green circles are your teammates, and red your enemies.
The lines are ganking routes.
And the numbers are the order to jungling.

Teamfights:

Your role in a teamfight is grab with Thundering Smash the AD Carry like 1st priority, and squishy enemies like 2st priority. After that use Sky Splitter and lets fight with Stormbringer, ever frenzy enemies with less health or the weakest enemy.

Ranked Play:

In rankeds, you should go Solo top, or Bot with the AD Carry.
With any Ad carry you gonna go, you gonna make a good duo.

I hope this guide will be useful, and can play pretty well with Volibear.
Thanks to Klofta, which motivated me to make this guide.

Credits to jhoijhoi for the template, which you can find here.