The Tavern

I abyssed while in shoals due to a damnation deck pull. I ended up in a multi-level Snake-themed abyss full of naga.

The other S branch is Snake, and I did explore it down to level 5 (but did not complete it). I would have expected an abyss full of Shoals-themed items if anything, not naga.

Is this just RNG or was the game attempting to present a theme?

I've encountered snake-themed abyss areas, a couple other "themed" abyss areas as well, I don't think it has anything to do with what dungeon branches are generated.

The abyss sometimes hits streaks of nearly making sense, mimicking branches.

I once happened upon an abyssal Orb of Fire! Managed to kill it, fortunately

Can abyssal oof happen normally?
Because if it can this abyss "reform" has hit a whole new low.

I ran into an Abyss that was mimicking Slime at one point. It was a nonstop barrage of acid blobs and azure jellies, and it made me want to cry.

Yes. Abyss now basically chooses a random level of a random branch and takes 2/3rds of its monsters from there. So it will frequently generate orbs of fire.

What the fuck, how is this in any way acceptable.
I mean the time I had sentinels and convokers spawn and they were everywhere was horrible, but random zot or slime monsters?

What? Has abyss changed again?
Now is is a mimic of other branches? Have old inhabitants been removed?
Plus, don't tell me zot's monster (especially oof) can *frequently* be meet in abyss:1

I also got slime monsters in the same abyss run as the OOF

The acid blobs were MUCH more of a PITA than the OOF. Meeting the OOF felt pretty cool, actually.

Psiweapon, when did that happen?
Apparently it was fixed some time ago, at least for oofs. No idea about slimes.

Looks like slime, blade, tomb, and zot were removed from the list (recently in the case of slime and zot). Also the level of the branch is deterministic, it's just chosen so that it might as well be random:
That was the case until this very recent change, yes.

Just out of curiosity, what's the thinking behind this change? Someone corrupted a level of that branch and sent all of its denizens to the Abyss?

In practice, it means any given floor of the abyss plays like an arbitrarily selected other branch with weird terrain and feels to me less chaotic.

Abyss is stsill going to be very different, since terrain is usually a lot more important than the actual enemies that you're fighting (unless you get orbs of fire or something, but that bug was fixed). In practice, you have a section where you've got lots of enemies from a specific branch but after walking away for a while it gets more random (this is just my experience, I haven't looked at the code). Anything that reduces the number of raiju and neqoxecs in the abyss is fine in my book.

Wait... THEY CHANGED ABYSS AGAIN!? NNNNOOOOOOOO!

I loved 0.13 abyss, that was the most terrifying and unforgiving place in crawl, it had the best flavor out of any branch!

apparently a design goal is to have all the monsters in the game able to appear anywhere in the game
there's no other reasonable explanation for adding snake monsters to depths

further support for this theory: minotaurs

Removing forty monsters, including a decent chunk of Lair, Swamp, and Crypt monsters, from late D, and incidentally increasing the proportional weight of naga that already could appear in late-D, counts as adding Snake monsters to Depths? News to me. I like empty disparaging of irresponsible dev principles and open declaration of bad design trends as much as the next cynic, but come on, letting particularly bad recent trends being an excuse of depression for being inaccurate ruins the lofty authority that makes the toxicity towards never improving the game work as a position in the first place.

-----------

Raiju and the abyss guests were both meant to cut into the commonness of two strategic-damage Abyss demons (neqoxec mutations and smoke demon sticky flame), both very easily arguably good designs for the endless, malformed terrain of the Abyss but clearly so unbearable that several months of brokenness (indiscriminate choices of any branch's floor spawn produce things like Lair chaff or excessively dangerous things like vault sentinels / ironbrand convokers and, yes, for a brief period, orbs of fire) were acceptable up until this point in comparsion. Even at 1/9 chance of guest choice per spawn, the potentially much higher chance of bands from other branches make it feel higher, and it explodes upwards when abyss shifts change the set without killing wandering monsters and produce a messy slew of random other monsters. Some pithy comment about karma would work here.

I've been doing some patches to address both this and abyss depth-scaling through heavy monster set tweaks, have another in the works, and even have a long write-up of a proposal (scroll down to "worldbinders") to preserve the variety and flavour of abyss guests while cutting into demons and actually looking for balance via a new monster that's been approved by several devs (not that I have the knowledge needed to code that last one myself). These, alongside some more subtle things (generate_awake shapeshifters in Abyss are very naughty, really) were meant to provide an alternative solution, not that the monster set changes are particularly visible with the current scenario, and if the last of these was done some devs have agreed it'd be enough to revert the abyss guests feature (again, not that I have knowledge of preserving save compatibility myself). Of course, this is clearly just as terrible in replacing some autofight-fodder with a long list of non-Abyss monsters, and introducing a non-lethal, complex summoner, so the community echo chambers can brush off my efforts as slightly-less-insane bits of ruination and move on to complaining about other things (like banishment itself or whatever).

(Also, there's a trivial possible change that could be done to sticky flame to make abyss smoke demons more palatable in reducing the pointlessly-high item destruction rate chance from 12% (yes, plenty of arguments can be made over making it 0%), but the last time item destruction itself was addressed the forums here exploded into a frenzy that thought it could actively change development by arguing itself into pieces, so whatever.)