|Floating horrors getting close to a forest, and turning away.|
Such a beast is horrible enough, but they tend to move about in swarming flocks, sometimes as many as hundreds across, covering acres and acres of country side (they spread out, and their tentacles can cover a patch of ground some 30' x 30' underneath them, and extending 20' in each direction). The swarm will move over the land, attempting to avoid extremely rough cuts and cliffs, and also forest, but otherwise not stopping. Occasionally, a floating horror will collide with a large stone structure and become ensnared there, while it's tentacles search out inside the building looking for prey and food. Most smaller buildings, or those made of materials less dense than iron or stone, will be bumped into by the floating horror, and it will slowly bobble over the structure, damaging it with their acidic tentacles, and making a meal out of whatever living that they encounter along the way.
Electricity, fear, hold person or hold monster, paralyzation, polymorph and sleep based attacks will have no affect, the same as with gelatinous cubes (see standard reference here). Fire and heat based attacks entitle the floating horror to a saving throw vs. magic, and if failed, will do a maximum of 1d4 points of damage.
A strike by a tentacle will cause the victim to make a save vs. paralysis, or be paralyzed for 5-20 rounds. Regardless, a strike will do damage (see below). Every 5' square within the 30' x 30 area covered by the tentacles is attacked once each round. There are simply too many tentacles to effectively remove them, without killing the floating horror.
All normal weapons do damage, but thrown or missile weapons are then lost inside the floating horror, to be retrieved after combat. Wood and leather inside the floating horror takes days to be decomposed by the acidic jelly, so recovered weapons that have only been inside a short amount of time should be okay. Metal and gems are not affected, making the floating horror that has recently been near a populated area likely to contain treasures (as per the gelatinous cube, again).
The biggest danger floating horrors pose is that they are completely and utterly silent, and largely clear, making them extremely difficult to spot in anything but pure daylight. A settlement that is aware of them, can ward them off (usually) with fire and long polearms. A settlement that is overrun without warning will only react with the first horrific screams of acid burns from tentacles, and the disappearance of livestock and family members up into the floating horrors.
Num Appearing: 2d6 (minor group); or 1d6x100 (mass migration - very rare)
Armor Class: 7
Hit Dice: 4hd
Attacks: 1 attack per 5' square, in a 30' x 30' area - tentacle sting
Damage: 1d6+2; save vs. paralysis (if fail, then par. 5d4 rounds)
Morale: not applicable