Lionfish (Pterois)
Predatory marine fish with poisonous spines. Beautiful but not reef safe: eats shrimp, crabs and small fish.
Detailed explanation
The lionfish (Pterois volitans) is spectacular but predatory. Eat anything that fits into your mouth: shrimp, crab, small fish.
The spines of the dorsal fin are poisonous. The sting is very painful (similar to an intense wasp sting). Dip your hand in hot water (45 degrees) to denature the poison.
Requires large aquariums (300+ litres) with appropriately sized companions. It is not reef safe for predation but does not touch the corals.