This is prob the first thing u thought of . ( i m right ) . Well this is because volibear offers the team as a damage soaker and damage dealer ( especailly from early to mid game ). U gain a huge power spike at 6 , and u could lierally 1v1 anyone once u hit 6 and have ur passive. Volibear of course , snowballs entirely from 1 kill and could literally carry games all by himself.

Volibear is a Bear . U just need to remember that , and congrats u r on ur way to diamond .
What does being a bear means? It means u need to kill anyone that gets in ur way. Remember that as well. This means that u dont have to give a **** about ur jungle farm and just gank repeately once u obtain your blue and red buff . U dont wanna waste all ur time in a jungler ( Its global warming now man ) , and instead just focus on killing enemies. yes , your first 18 minutes on the game is literally focus on killing ur enemies , just gank and gank and gank and gank ( voli is a soild ganker ) till the enemy team ff20 or just afk. Yes this method doesnt work beyond diamnd 3 as ppl tend to be damm paranoid n can read ur movements easily.

Ok lmma just summarise this part to save time.
Runes
Focus on attack speed reds , amour seals , Cooldown Glyps , and movespd Quints

Masteries
Take anything that incease ur power as a bear ( thats all )

FOR VOLIBEAR U MUST MAX W AT ALL COST , NO COMMENT.
Then Q and E ( the ultimate question ) , well i prefer taking E for the higher dmg and slow as to compared to Q , u already have movespd quints, Q is just a ultitly spell , nothing more , nothing less , and trust me u can outrun ur oppenents with a lv 1 Q and lv 1 boots.

For items ( there r usualy 2 situations where the builds r very diffent)

FOr winning ( meaning that u have MORE OBJECTIVES ( not kills ) and that the enemy Caries do little to 0 impact.

U RUSH A ACICENT GOLEM ( FERAL TKES A LONG TIME TO STACK AS VOLI )
GET A PHAGE N A GIANT BELT
ANd ofc evlove UR PHAGE TO TRINITY FORCE N GIANT BELT TO SUNFIRE . and make sure to get a warmog , UR BEAR BITE deals immense dmg once u have more than 2.7 k hp , dont underesitmate it.

AND WHEN U R LOSING
BUILD FULL TANK DUH , U R LOSING

of couse , volibear offers a differnt play style to ur team and thus doesnt really stand out , but hes is literally easiest way to plat at the very least.

PROS:
W DOES INTENSE DAMAGE
SNOWBALLS VERY HARD
CAN duel Early invades by enemy junglers ( lee sin )
OHHH DAMM THAT PASSIVE HEAL WITH WARMOG AND Spirt VISAGE ( mundo gtfo )
Strong ganks ( CAN CATCH UP EASILY AND DEAL ALOT OF DMG AS WELL)

Cons:
CAN BE KITED EASILY ( screw u vayne mains )
Kinda underwhelming late game if u r not ahead
Ignite Or Grivious Wounds counter u kinda hard
Can be chase down kinda easily ( low base movespd )
Global Warming killing him off

of couse , there r champions that can screw volibear over. here r a few

U kidding me bro? u r a bear just fight whoever that come to ur junglers just kidding lol

Elise ( 7/10 )
Its not everyday that u see a spider taking down her bear , but spiderwoman is a diffenet story. HER Q ABSOULTELY WRECKS U OVER AND SHE DOES MORE DMG THan U in spider form . ( humliating..)

Lee Sin ( 6/10 )
THis could go either way , depends wherehter the lee is a good or bad . ( u either be good at lee sin or u r bad at lee sin , theres is no moderate )

Darius (7/10)
Deals more dmg than u at all stages of the game ( unless u r fed ) , his ulti will wreck u when u r at 15% HEALTH , dont bail on ur passive saving u , no chance.

IF U R bronze , sliver or gold. Just play volibear , u can easily get to plat. Most low elo ppl haven caught on the fact that volibear can easily wrecks their entire enemy team once he is fed , dont waste too much time farming , spent like 20 percent farming and 80 percent ganking , if u fail yes , u will be underlv , but if u succeed tax a wave or 2 to not fall behind and cover a lane if neceesary , ur clear spd in the jungle at early lvs is wayy too slow.