Volibear trained by Olaf

One day Olaf and Volibear are hanging out in the Freljord.

V: "Olaf, I am depressed..." O: "Yarrrr! V: "I am a great champ but no one plays me in pro games."

Olaf then stands and behind to instruct Volibear in the greatness of Ragnarok. Volibear slowly behind to understand it and (changes at bottom):

Rolling Thunder Cost: 40 Mana Range: 300

Volibear drops to all fours and runs faster. This bonus speed increases when chasing enemy champions. The first enemy he attacks is thrown backwards over Volibear.

Volibear drops to all fours to hunt his enemies, gaining 15/17.5/20/22.5/25% Movement Speed for 4 seconds. This bonus is enhanced to 30/37.5/45/52.5/60% Movement Speed while moving toward enemy champions.Volibear's next attack during this time deals an additional 30/60/90/120/150 physical damage and flings the target behind him.

NEW: for each level Volibear puts into in Rolling Thunder he becomes unstoppable and immune to CC for 1 second (just like his good buddy Olaf in Ragnarok). Level 1: immune to CC for 1/4 seconds of Rolling Thunder ... Level 4: immune to CC for 4/4 seconds of Rolling Thunder

O: "Now we walking with Thunder!"

I mean, after all, he's A BIG BEAR!

EDIT: maybe Voli is only immune to the first CC after calling Rolling Thunder if that's too powerful.