Is a narwhal an omnivore or a herbivore or a carnivore?

No. Carnivores only eat meat. Herbivores only eat plants. Omnivores eat both meat and plants. The great white whale is a carnivore. It eats small fishes, seastars, octopuses, krill and other aquatic invertebrates. Great white whales are mammals. Humans, dogs and cats are the only omnivorous mammals.