So I did a quick (and quite rough) sketch of Volibear from the written description / interaction with Udyr.
"In the forest behind Najak, the great black-leaf trees cracked and shook. Taller than a mammoth, it stepped out of the woods. Walls of muscle, each limb larger than a man, propelled the beast forward. Its broken, ancient armor of dark, metal plates was caked brown by the dried gore of a hundreds of battles. Broken weapons, rusted with age, jutted from its back and shoulders. One half of its face had been stripped of flesh, revealing oily bone, teeth, and horns. From its mouth, an unnatural, black blood dripped. Its four eyes, impossibly ancient, alien, and pitiless, looked over Sejuani and Udyr."
"Udyr climbed up the rubble of a stairway to a ruined square. Surrounded by tall stone buildings, he found the monster waiting for him. Alone and in the middle of the city, the bear spirit’s avatar impaled corpses on stakes arranged in some unknowable pattern. Black branches and roots grew from the speared bodies around the beast, like worms slowly crawling from the earth. The flesh and fur on the Volibear’s face had healed, it’s muscles seemed thicker, stronger than before.
The Volibear’s eyes turned to Udyr as the shaman approached. Across its face, a dozen new eyes bloomed, each as dark and cold as a spider’s. Perhaps it smelled the foreign magic on the Winter’s Claw shaman, and now deemed him worthy of examination. Somehow Udyr knew, this time, it spoke to him alone.
“I will be reborn. You cannot stop that, son of man,” the beast said.