Tentacles

Introduced in v1.0.8, Tentacles are dangerous mobs that will grab and pull the player below the surface of the quicksand type it is in. There are currently two types of tentacles, Mud Tentacles and Nether Tentacles (Swallowing Flesh)

Spawning
Tentacles don't normally spawn like other mobs, instead they spawn if another mob or player walks into the quicksand type it can spawn in. As of v1.0.8.8, tentacles can only spawn in Bottomless mud, Soft quicksand, Jungle Quicksand and Swallowing flesh.

Chance of spawning
Mud Tentacles spawn in the Overworld, in Soft Quicksand and Jungle Quicksand and even more rare in Bottomless mud, but in specific "Tentacles chunks".

Nether Tentacles have a 100% chance of spawning in Swallowing Flesh.

Tentacle chunks
Similar to vanilla Slimes, Mud Tentacles spawn throughout the world in the wide (at least 3x3) and deep (at least 2 blocks deep) quicksand pits, but only in certain chunks with chance regardless its type: These "Tentacles chunks" are determined pseudo-randomly by combining their chunk coordinates with the seed of the world. So if the player finds a pit with Mud Tentacles, then exactly that pit or any pit in same chunk satisfy the conditions will for the quicksand type to inhabit by Mud Tentacles.

Although, there is other method when seeking Mud Tentacles, without dipping in the pit (and getting stuck) or sacrificing a mob. Mud Tentacles have unique behavior in relation to certain items, food items in particular which could be dropped in the pit that satisfy the conditions needed. Upon dropping a piece of food (primarily meat based, or rotten flesh) have a high chance to be instantly swallowed by Mud Tentacles, which is indicated as loud splash on the surface. This method is the clearest way to mark dangerous pits and tentacle chunks as well.

Appearance
Mud Tentacles are green in appearance while Nether Tentacles appear flesh pink in color.

Behaviour
Tentacles behave in a unique way. When a player walks into the quicksand type, tentacles will start to come out and grab the player around the legs before grabbing the waist and slowly pull the player down below the surface. The tentacles are extremely strong and grip the player no matter what the player does to try and escape. Even flying in creative mode cannot break the grip of the tentacles as they can only fly roughly 1 blocks high before the tentacles resist and will eventually drag the player back down relentlessly. Despite the strength of the Mud Tentacles, they are unable to pull the player under if they are a wearing life jacket.

Sometimes however, there is a chance that if in creative mode (or creative mode flight mods in survival) and the player has been grabbed, they may be still be able to fly away free if the tentacles did not bring them deep enough. This is noticed if one were to keep holding down space bar (to increase height in creative mode), the player keeps going up instead of being dragged down.

Also worth noting is that even though the tentacles are extremely strong, they do not reach full strength upon grabbing the player, so the player has a small chance of still being able to escape. Though the tentacles will pull down any player with creative mode flight attempting to hover.

Escaping the tentacles
Because the tentacles are extremely strong, escaping the tentacles normally by using rope, grappling hook, long stick or even creative mode flight is next to impossible as the grip is too strong. However this does not mean it is inescapable, there are a few ways to escape the grip of the tentacles:
 * Destroy the source block that formed the tentacles, though this is only possible in creative mode and is not really a fun way to escape
 * Killing the tentacle, but this is extremely hard to do as most of it is in the quicksand type and cannot be hit even by potions. Even still, the player gets the fatigue and Mining speed debuff, making killing the tentacle much more harder.
 * Teleport using commands or using an ender pearl, by far the easiest and fastest way to escape the tentacles though the former is not possible if the world (or server) doesn't allow commands.
 * Flying sideways, if the tentacle has gripped the player but has not dragged the player low enough for their legs to touch the quicksand type, they can fly in another direction while going up. This will break the grip of the tentacle easily.

Other effects
Aside from pulling the player under, the tentacle will also give the player a fatigue and mining speed debuff of unknown level.

Trivia

 * The tentacles usually reach full strength the moment the player sinks waist deep in the quicksand types that can spawn it.
 * Despite what it seems, the tentacles have a surprising reach upon spawning to grab the player. This can easily be seen if the player in creative mode spawn of the tentacle and increase in height slightly, as of current the tentacles can grab the player up to 1 block in height upon spawning before losing interest in grabbing the player.
 * The tentacles consist of both 2d and 3d parts.
 * The 2d part is the tentacles themselves which appear to be four tentacles
 * The 3d part is the part of the tentacles that grabs the player.
 * Mud Tentacles are not as strong as Nether Tentacles.
 * Nether Tentacles are also much more agressive as more often then not they will actively pull the player in even as they attempt to escape.
 * They willl also sometimes be so strong that the moment the player is grabbed, escape is not possible. This is easily tested in creative mode.
 * It is odd that the tentacles give the player debuff effects even though it is simply grabbing the player. This might be supposed to represent that the tentacles actually has grabbed around the player's arms as well instead of just the waist.
 * When the player in creative mode (or creative mode flight mod in survival) attempts their futile escape after the Mud Tentacles from Jungle Quicksand has grabbed them, the quicksand's surface may rapidly bubble.
 * Tentacles can vary from size to size depending on how big the mob was.
 * Apparently, if Spiders gets grabbed by the tentacles, the tentacles are extremely huge and instantly suck the mob under.
 * Mud tentacles can also spawn in thinnish mud and deep mud in tentacle chunks that allow mud tentacles to spawn in bottomless mud. Upon doing so, all mud blocks in a 3x3 radius around the player/npc are converted into bottomless mud, allowing the tentacles to drag them under.