Yeah, I know once again I’m rant about Jardobah. Well the most recent episode inspired me to make the Ethereal Kraken. This is a really nasty beastie that can screw up a party in more ways the one.
The Ethereal Kraken is an ambush predator. It’s vulnerable bits sit safely in the next dungeon room or even the room above or below the one that the characters are exploring. It can reach its tentacles through the walls, floor, or ceiling to grab at its food. Here’s the stats.

Ethereal Kraken
Hit Dice: Main Body: 7/Each Tentacle 2
Armor Class: Main Body: 4[14]/Each Tentacle: 7[12]
Attacks: Main Body: Crunchy Beak (2d6)/10x Tentacle: (1d6)
Saving Throw: Main Body: 9/Tentacles: 16
Special: See Through Walls, Half Damage From Non-Magical Weapons, Construct (Automatic Damage after successful attack with a tentacle. Saving Throw to escape), Pull Through the Wall (When the Ethereal Kraken has a poor character in its tentacles, the beast may attempt to the character through the wall. The character attempts a Saving Throw. If it fails then the character passes through the wall and is now in the primary lair of the monster. If it is successful then the character doesn’t pass through the wall but the tentacle does. Smashing into the wall causes 1d8 damage but frees the character from the tentacle), Regenerate Tentacles (It can regenerate in a tentacle in 3d6 Turns).
Move: 6
Alignment: Neutral
Challenge Level/XP: 11/1,700 (4/120)

As you can see, encountering an Ethereal Kraken is basically fighting two monsters. Chopping off tentacles doesn’t kill the monster but will make it mad or cause it leave a group alone. The only way to actually kill it, is taking out the “main body”. As a GM, you can see how deadly this thing can be. It can separate a party in the middle of an already dangerous dungeon so it may be worth a few XP than I indicated above.