Merm/Normal

Merms are slightly aggressive mobs, which usually spawn in Marshes. They live in Rundown Houses. Merms will try to attack if the player gets too close to their house, or to them when they are far away from their house or their house destroyed. Similar to Pigs, when they are provoked, they will attack their provoker in groups. They will drop living Fish and Frog Legs once they are dead.

Appearance
They use a similar hunchback model like the walruses, pigs and bunnymen. They have gills on the sides of their heads and down their neck. They have bulging eyes, a gaping mouth, and are covered in fishy scales.

Spawning
Merms spawn from Rundown Houses, which randomly appear in Marsh Biomes. A Rundown House can house up to 4 Merms, and respawns a Merm in 4 days after it's killed. During the day only 1 Merm per Rundown House is normally outside (unless it gets into combat, then all other Merms come out), when dusk comes all Merms go outside.

Strategy
They have the same Kiting AI like the other hunchback mobs, so the same strategy with Pigs is recommended with Merms.

They take two blasts from the Ice Staff to be frozen.

You may also want to visit the Merms, as you may spot Tentacle Spikes, Tentacle Spots and even Silk left behind after Merms have finished off Tentacles and Spiders in the marsh biome.

Trivia

 * "Merm" is actually short for "Mermen".xD
 * Merms are based on "The Deep Ones" from Lovecraft.
 * Kevin answered the question "Why Merms drop fish?" in the ShannonZKiller's Pre-release twitch. The answer was "They are made of fish."
 * A good way to get Tentacle Spikes/Tentacle Spots is to lure merms over to Tentacles and they will slowly kill them.
 * Merm Heads are random structures that appear in Pig Villages.
 * Pig Heads, as of The End is Nigh update, spawn in Merm villages. This suggests some kind of hostility between  the two tribes of animals. Similarly, Merm Heads spawn inside some Pig villages.
 * When Merms are spawned in via Console, they will always attack you even if you are standing still.