A qualitative Black Pudding

 Next monster by alphabetical order of the Little Brown Books is the black pudding:

‘Another member of the clean-up crew and nuisance monster, Black Puddings are not affected by cold, it is spread into smaller ones by chops or lightening bolts, but is killed by fire. Black Puddings dissolve wood, corrode metaI at a reasonably fast rate, have no effect on stone, and cause three dice of damage to exposed flesh. If an armored character runs through a Black Pudding the monster's corrosive power will eat away the foot and leg protection of the armor so that it will fall-away next turn. Black Puddings can pass through fairly small openings, and they can travel as easily on ceilings as on floors.’ (Monsters and Treasure p.19)

Amount encountered: 1; AC 6; Movement: 6; HD: 10; Never in a lair; Never has treasure (Ibid. p.4)

Information I find notable:

• The LBB give us not only the functions of black puddings in their interactions with the environment (what it does and does not corrode, how it interacts with certain elements, how it moves), but also its function in the dungeon: ‘clean-up crew’ (its in-world ecological niche) and ‘nuisance monster’ (a suggestion for the referee for when and where to use it). 
• We get some idea of what it looks like based on the description of what happens when an armoured character runs ‘through’ a black pudding (suggesting a literal pudding-like consistency and a height of about the knees of an average human). 
• It is always encountered alone, which is interesting given that it is a scavenger. Rats and vultures congregate around a source of food, but the pudding is always alone. This makes it seem to me that black puddings can merge with each other, which makes sense to me given that they can be split.
• I am surprised by how mobile it is. I expected the hole-squeezing and it makes sense to me that it can move on ceilings, but it is way faster than I would have thought. The fact that it can keep pace with a dwarf (even while on the ceiling) is disgustingly terrifying. 
• This version of the pudding is also extremely hardy. Ten Hit Dice puts it in the same ballpark as Balrogs, Efreet, some Giants, and some Dragons. That is crazy for a ‘nuisance monster’. Its mediocre Armour Class means it will be hit more often, but it is still way more durable than I thought it would be.
• Nowhere does it say that black puddings are not intelligent. Might mean nothing on the whole, but given that it was spelled out for the Basilisk it is surprising to me. Especially because (at least to my knowledge) this is a D&D original.

All in all, it's giving this:


 

‘This’ being a plasmodial slime mold, a single cellular organism that can merge with others of its kind, split apart, is surprisingly good at finding optimal solutions for problems, and is definitely part of nature’s ‘clean-up crew’. 
Considering the black pudding as a slime mold has some advantages as it allows us to take the rest of a slime mold’s qualities and apply them to black puddings to give them a bit of extra flair. 
For example, slime molds can survive prolonged periods of dehydration and malnourishment. Just add water to turn the grey shriveled film into a horrifying black goop. 
Their lifecycle is also quite interesting. The way they produce spores once they run out of food could be wonderful dungeon dressing, a classic hazard, and/or a warning to the players that this has relatively recently seen pudding activity. 
Finally, slime molds leave behind a residue which tells them where they have been. This too could be a fun way to indicate the presence of a black pudding and give you something to present to players when ‘tracks’ are rolled on an overloaded encounter dice. Additionally, as this is a way for the pudding to know where it has been (and where there probably won’t be any new food), it can also communicate relative safety from the pudding to savvy players. (source for info on slime molds)

So this is what I ended up with:

Black Pudding: 

Traits: 

• wide (like carpet), amorphous (like water balloon), crawling (like spider). 

Strengths: 

• Corrosive Touch: Contact will dissolve most metals and all organic matter. Residue needs to be washed off to prevent effect lingers after contact. 
• Splitting: Attacks that would cause cutting or cleaving instead cause it to split in two independent puddings of appropriate size. 
• Antifreeze: Able to withstand even extreme cold. 
• Cunning: Adapt at coming up with optimal ways to safely secure food, including approaching from above, hiding in hollows, pretending to be ordinary muck in shallow puddles, prioritizing torchbearers, etc. 

Weaknesses: 

• Flammable: Is only truly hurt by fire. Once set ablaze it will attempt to split in two and flee. 
• Food motivated: All it cares about is nourishment, making it relatively easy to manipulate. 

Ecology:

• One and Only: When two meet they will merge into a single, bigger specimen.  
• Draft Migration: Once it has grown to sufficient size it will find a drafty area of the dungeon and create spores. The temporary forests that grow this way are both a hazard and a source of food for others in the dungeon.