As an additional cost to cast Corpse Lunge, you exile a creature card from your graveyard. When Corpse Lunge resolves, damage equal to the power of the exiled creature card will be dealt to the targeted creature. It is important to note that the source of this damage is the Corpse Lunge itself, and not the exiled creature card.
For example, if you cast Corpse Lunge targeting an Elite Inquisitor and exiling a Walking Corpse, the Inquisitor will be dealt two points of damage. It doesn’t matter that the Inquisitor has protection from zombies because the source of the damage is Corpse Lunge, which has no subtypes.