Mantis Shrimp- must be kept alone, and you can't get your hands near them or bye bye finger.
Coral Banded Shrimp- not as aggressive as mantis shrimp but will pick on other inverts and fish.
Cuttlefish- will eat all shrimp, crabs, and fish it can catch.
Octopus- (same as cuttlefish)
Sallylightfoot Crab- again, not extremely aggressive but picks on other inverts.
Camel Shrimp- again, not extremely aggressive but picks on other shrimp.
Saron Shrimp- Extremely destructive and aggressive to most other inverts and sometimes fish.
Cave Shrimp- (same as coral banded shrimp)
Bobbit Worms- THE MOST AGGRESSIVE AND HORRIFIC ANIMAL TO ENTER A TANK! I'VE HEARD STORIES ABOUT THEM TRYING TO EAT ROCKS BECAUSE THE LOOK LIKE FOOD ITEMS.