From an in-game perspective, I'd suggest not teaching Inferno altogether. You already have 5 Fire type moves which are actually really good, but even with Victini's Victory Star Ability, Inferno will only reach a 55% accuracy, which is just plain unreliable.
In the future, try dropping some Fire Moves to make sure Victini is more useful. You've already missed out on Zen Headbutt, which it learns at level 47, but maybe you can get the Move Reminder in Mistralton City if your playing Black/White or The Pokemon World Tournament if you're Black2/White2. In exchange for a Heart Scale, you can get your Victini to learn Zen Headbutt.
Good luck my friend! :D