False Cleanerfish

Found singly, pairs, or in small schools, often to be found in small holes and empty worm tubes, over lagoons, reef flats, and outer reef slopes.
They copy the look and swimming style of cleaner wrasses to get close to larger fish, but instead of cleaning they bite pieces of fin and tissue. They will also nip divers.
Large adults only do this as a hobby, other times they feed on benthic invertebrates and zooplankton.
Widespread East Indian Ocean, Pacific Ocean

Combtooth Blennies are the largest family of blennies, found in both tropical and subtropical waters and freshwater habitats, as the name suggests they have comb like teeth lining their jaws, well suited for scraping food off hard surfaces!
Sabretooth Blennies have teeth to match their name!
They can be seen darting forward to sever flesh from fishes fins. (can sometimes be seen taking a swipe at divers as well) They will then dart back into their holes out of harm's way.
Some blennies will mimic cleaner wrasses to get close enough for a nip at fish.
A few Sabretooth Blennies are venomous.