Mermaid

The mermaid is a neutral ocean mob that attacks anything that attacks it, or attacks another mermaid. Mermaids spawn underwater, so players may have trouble hitting them. Mermaids normaly spawn in groups that have up to 7-10 mermaids, but rarely they can spawn alone.

Statistics
Health: 10 hearts (20 health)

Spawn: In water (including underwater structures)

Attack: 3 hearts (easy) 5 hearts (normal) 8 hearts (hard)

Drops: 3-6 Sea lanterns, 1-8 Prismarine shards, 1-2 salmon and rarely a diamond sword with awesome enchantments on it, probably called the Aqua Sword.