It is a Naso Vlamengii - gets big
All Naso Unicornis get horns but not until 6-9 inches in length. Their horn is fairly short - not past the snout
All Naso Brevirostris get horns as well. The horn extends beyond their mouths.
Both are often called "unicorn tang" in the hobby.
Vlamengii grows a large bump on his nose.