When “Inferno” battles with another monster with equal ATK, “Inferno”’s effect is not activated because it must destroy the other monster “and send it to the Graveyard”, and at that time, Inferno is no longer on the field to activate its effect.
If “Inferno” attacks a face-down “Cyber Jar”, “Inferno” is destroyed by the effect of “Cyber Jar” and “Inferno”’s effect is not activated.