After verifying, it turns out you're right: I completely forgot about this power-up. It would've been a nice addition. "Invincibility Fire Wheel" and the attack "Art of Fire Wheel" use the same sprites, so the only ones who go unused are its icon and HUD icon: Oh, and this jump sprite goes unused as well: They should be added to the article.
In NG 1, the IFW is used automatically and can only be used once. However, in NG 2, it uses Ninpo and can be used as many times as you desire (if you have the Ninpo).
