In situations where you battle creatures that are immune to fire, this ability is useless. In some cases, it's even detrimental if fire can heal the enemy. So, I propose the following idea:

Inferno Shot changed to "Imbue Shot" and functionality changed

It does the same type of damage as the imbue does.

Imbue shot = fire if fire arrows
ice if ice arrows
acid if corrosive arrows
electric if electric arrows
poison if paralyze arrows
untyped or psionic if terror arrows