Tentacle

Tentacles are hostile Monsters that live in Marshes or in Caves. They appear as purple, spiked tentacles coming out from the ground which will attack anything that comes close enough. They take three blasts from the Ice Staff to be frozen. When killed Tentacles will drop 2 Monster Meat and can drop either a Tentacle Spike or Tentacle Spots. However, once killed they will never respawn, making both of those items Non-renewable resources.

Behavior
Tentacles can only be seen once a creature or character gets relatively close. At first there will be a barely noticeable swirling patch on the ground, followed by a small piece of tentacle that looks like a purple bubble which appears just before they strike. When a creature is in range the Tentacle will emerge and twirl around once before  snapping and standing straight up. There is a brief delay before they will strike again. If its target moves out of range the Tentacle will sink back down into the Marsh ; they cannot move around and give chase. Sometimes after attacking Tentacles will stay hidden until all targets move out of range, at which point they begin to behave normally.

Hunting
Tentacles are very dangerous because of their high damage and health. If you aren't careful, you can walk straight into tentacles and they will take a chunk out of your health. They cannot be stunlocked and will continue to attack as long as there is something within range. It takes 15 strikes with a Spear to kill a Tentacle. If properly timed they can be attacked in between their strikes, but this is difficult to master. Tentacles are immune to Sleep Darts and Pan Flutes, however Bee Mines are very effective against them. They also cannot be burned with the Fire Staff. Although they appear to have an area attack, Tentacles actually attack targets individually. Due to this limitation Pigs that attack them if they get too close can easily kill a Tentacle if there at least 3 of them.

It can be easy to kill them with little or no work, by finding some Rundown Houses, waiting for dusk, and seeing if the tentacle alarms  the Merms. The stiff fight will end in Frog Legs, Monster Meat, Fish and maybe Tentacle Spots or the Tentacle Spike.

Big Tentacle
A Big Tentacle is a large section of a tentacle found in Caves.

You are able to attack it's underground section, doing so will cause a bunch of other tentacles to spawn and die in one hit. When defeated, the tentacle will retreat into the ground, causing an earthquake. It will leave behind a hole.

The hole can oddly be attacked, and the big tentacle will rise again, this may be a bug.

Trivia

 * Wolfgang with a tentacle spike (strongest character and 2nd strongest weapon ingame) can kill a tentacle with 7 hits.
 * If the player is near a swamp biome, the Tentacle can appear (rare) outside of its biome and will attack.
 * Due to their aggressive nature, it is common to find drops from creatures they kill or from dead Tentacles killed by other creatures (usually Merms) lying on the swamps. They can kill a group of 4 spiders on their own.
 * Tentacles will not spawn beside world-generated Roads.