holy ****.... someone go get a paladin 

It's basically a slug. Baking soda melts them.

Yes, so long as the spell in question doesn't require an INT of 3+

This was the first creature we encountered in our campaign. For some reason one of us split it by yelling “I am a Belmont!” and then they shot it with their crossbow after we weakened it. The outcome the DM described was very gruesome. It’s a strange world.

no

Quote from nonbiri >>

The illustration shows, and the description talks about, the Black Pudding engulfing its victim, like a Gelatinous Cube, but unlike the cube, there is no Engulf attack in the pudding's stat block. Was this just an oversight? I've got an encounter with one coming up, and as DM I'm thinking of borrowing the Gelatinous Cube's Engulf attack. Not sure yet if I'd use Engulf "as is" or modify it a bit.

 i'd give them the grappler feat or something similar

Unless it says its immune to psychic damage, it isn't immune to psychic damage RAW unless the spell or ability states it doesn't affect creatures with low INT. If you want it to be immune for any reason, you can make it so, but it already has so many immunities that you should increase its effective CR to 5 if you do so.

It does show it engulfing an ogre and the official black pudding miniatures are designed for a medium creature miniature to fit inside it, so I don't see any reason to not give it engulf from the gelatinous cube, but it should definitely do more damage because black puddings are more corrosive than gelatinous cubes. The GC deals the same damage as its pseudopod when it engulfs a creature and twice that at the top of each of its subsequent turns. So 18 (4d8) acid damage when the pudding engulfs a creature, and 36 (8d8) acid damage at the top of each of its turns; probably with a DC 15 instead of 12. This clearly makes the pudding way more powerful, so adjust the pudding's CR accordingly.

You could also always just let it enter another creature's space and try to grapple them when it does so, maybe with 18 (4d8) acid damage at the end of each turn they stay grappled.

a base can neutralize acid, baking soda is commonly used for this is school science labs

Interesting idea courtesy of Garrow. 

An encounter with a clay golem covered in a black pudding. Clay is a form of stone depending on the DM's interpretation so it would be immune to dissolving. But the real kicker is the golem's acid absorption. 

"Don't telegraph the ooze until it's been a round or two tho. Just describe it as a clay golem, with cracks filled with a blood-like tarry substance visible only through its reflecting the light of their torches.
Which will in turn, punish overeliance on darkvision, cuz in shades of gray, the pudding will be completely invisible. 
They'll be completely unable to target the thing unless they 1) have a light source and 2) pass a DC 15-18 Perception check to notice the lashing pseudopod"

Acid Absorption. Whenever the golem is subjected to acid damage, it takes no damage and instead regains a number of hit points equal to the acid damage dealt.

ta bueno pa las minas

Yum 

I am streching this over a door so the PC's have to kill it to escape the dungeoun

Longsword? Beyond useless. Rapier or arrow? Thumbs up.
okay? I'd give it resistance to piercing.

What if you split a simulacrum polymorphed into a black pudding?

Yess

f crash

Eh, the damage itself is negligeable, the problem i find is sending it against them when they dont have magical weapons. They get 5 hits before weapon is gone. Usually gets ended by spells, but melee is still viable, although not the best option.

I just nearly completely killed our monk with one lol

Baking soda neutralizes acid.  An open question whether real-world chemistry works in D&D, though.

So, on treasure, how is that figured? There's nothing in this to say what kind of ooze dissolves what (what would be left?) so my DM is denying there would be any treasure, won't even roll a die.

Description even says: "Since not every ooze digests every type of substance, some have coins, metal gear, bones, and other debris suspended within their quivering bodies. A slain ooze can be a rich source of treasure for its killers."