Honestly I would just like to see his passive and ult reworked somehow.
Passive - Increased health regen based on missing health outside of combat; increased lifesteal during combat based on missing health during combat. Plays on the duality of him as a mystic and a warrior in his lore.
Ult - Passive: Dealing ability damage heals Volibear based on his missing health.
Active: Same, but allow for an attack speed steroid and possibly a damage buff that applies to targets with certain health thresholds.
Right now, his ult does not live up to what it does in his biography. There, he calls upon his newfound power to come back from certain defeat against the Ursine Triumverate, ascertaing his place as their chieftan. In game? It tickles.
Otherwise, his abilities are good.