The Horned Heniochus, Heniochus varius, has a black bottom half that gradually turns to yellow and a small projection resembling a horn the the brow. They are very peaceful and can be kept with other peaceful fish, but may become aggressive towards other Butterflies with a similar pattern or coloration in smaller tanks.
They are also not reef safe since they will nip at and eat soft corals and stony polyps as well as ornamental shrimp, tube worms and anemones. Diet should include a variety of mysis and vitamin enriched brine shrimp, spirulina, nori, seaweed, marine algae, and algae based foods, 2-3 times daily.
So cool! The seem to do real well, acclimate fast & start eating very quickly, as long as you don't have boisterous fish. Introduce them early, or with smaller or calmer fish. If they are stressed they'll probably just keep hiding, won't eat, and waste away. Very cool & hardy fish once acclimated, tho