Aurelius

As an aside, here's why I avoid using pass use action on linedefs (second paragraph).

One thing to note about generalized line actions is that setting the 'model' field to 'numeric' allows monster activation. There are some caveats to this, but considering the generalized floor action 24802 in your screenshot is of the numeric kind, it's a possible culprit. You can read more about it in the HTML Boom reference (you can search for "generalized floors (8192 types)" to find the right spot, or go to Section 13 and scroll down a bit).

With UDMF, you won't be hitting any practical limits any time soon, given the size and geometric simplicity of your map. This glitch happens occasionally, most often with sectors that have a complex shape. It usually helps to divide the offending sector into smaller, simpler shapes. Doesn't have to be a lot, just a few splitting lines near the problematic section will probably help.

ClearLineSpecial can be used to clear the special of the line that activated the script. It can't be used on other lines though, for that you'll need to use SetLineSpecial as you mentioned. The usage is pretty simple, just follow the example on the wiki page. The first argument is the line id, second one is the special you want to give that line and the rest are arguments passed to that special. It'll override anything that was there before. However, if you're interested in activating/deactiving the line without altering the special, you can use SetLineActivation to change/remove the activation flags. They can then be returned with another script if needed, without having to redefine the special. Check the wiki examples again for proper usage.

In UDB, when a thing is added to the map, it retains the flag configuration of the previous thing that was added. So after you added your secret soulsphere you likely added a pinkie and two imps nearby without realizing they would also have the secret flag set. Another common way of accidentally adding secret sectors is to split a secret sector into multiple sectors without removing the "secret" property from the newly formed sectors. If you need to find all secret sectors or things in a map, you can go to Mode -> Find and Replace, then look for Sector Effect "1024" or Thing Flag "countsecret". A few sidenotes (I know it's a quick throwaway level, so if you're not in the market for mapping tips, just ignore the following):

While prefabs are fine, they're an unnecessary hurdle. There's also no need to have two instances of UDB open at the same time. Simply copy a section from a map, then open another map and paste it there. If you have conflicting tags, you can resolve the issue by using Paste special from the Edit dropdown menu.

@TasAcri Any more details on this?

In the DECORATE definition, you're using sprites called KEYPA0 and KEYPB0, but you've only included one called KEYP. This means your sprite name is missing the last two characters, which contain the frame and rotation info (A and B are the frames, 0 means there's only one sprite for all angles for that frame). You can rename your KEYP to KEYPA0, and supply another sprite for KEYB0 or just remove it entirely from the DECORATE definition and use KEYPA0 for both states, depending on what you want.

ACS_NamedExecute is a variant of ACS_Execute for named scripts. If you want to execute a named script (script that has a string identifier) inside another script, you need to use ACS_NamedExecute. It doesn't exist as an action special like ACS_Execute (action 80), so it doesn't have a numeric identifier (the action special 80 does allow named scripts to run too however, see the "Usage" section of the above link). SetThingSpecial can take both the name or the number of the action as an arg, so you can either write SetThingSpecial(tid, 80, 1); or SetThingSpecial(tid, ACS_Execute, 1); and they will mean the same thing. But as I previously mentioned, ACS_NamedExecute does not have a numeric identifier, so you can only write it as SetThingSpecial(tid, ACS_NamedExecute, "MyScript");

You can, like so: SetThingSpecial(tid, ACS_NamedExecute, "MyScript");

You can make a "composite" sky texture with two different skies stacked vertically, then use a displacement scroller to instantly scroll from one sky to another. This trick was used in Jumpwad MAP07. Here's an example wad using the MBF21 displacement scroller. Unfortunately this doesn't play well with GZDoom, though you might find some sky dimensions and/or offset to make it work. Alternatively you can add some GZDoom only alternative using LOADACS, but it's a bit more work.

Stabbey is correct, texture width needs to be a power of two. So numbers like 8, 16, 32, 64, 128, 256, 512 and so on. Height-wise textures can be up to 128 pixels tall, but are not limited to powers of two. Note though that if you have a vertically tiling texture that is not 128 pixels tall, you'll get the Tutti-frutti effect (same happens when using transparent textures on one-sided walls, 128 pixels tall or not). For textures that are power-of-two wide, I'd check the TEXTUREx lump you define them in to make sure everything is correct there (it should be if you didn't manually edit texture dimensions after adding them to the lump). Otherwise I really don't know what the problem could be. If you scrabbled together an example wad with the offending textures and share it here, along with the version of Crispy you're running, that'd go a long way.

While you were adding other sections to your map, you most likely inadvertently connected the two sides of the portal with a physical connection. You shouldn't do this, it'll turn the interactive portals visual-only (as you've experienced). Find where the physical connections are and replace them with portals. Funny enough, this is mentioned in the pinned comment of the DarkstarArchangel tutorial video on sector portals you posted a comment on only 3 days ago.

My solution is slightly different to Stabbey's. I'd use accelerative scrollers to do the pushing a voodoo doll to telefrag another voodoo doll to kill the player the door action itself to release the voodoo doll rather than have the voodoo doll open the door, so there's no delay in the door opening a walkover line to exit the map Telefragging the Romero head is an option that might in some cases be better to end the level, because a walkover exit line can theoretically be skipped. But you might want to make a custom DeHackEd thing that calls A_BrainDie on death, if you don't want the classic Romero scream on exit. Here's a quick test map showcasing both action 242 and the death exit mechanism you described. Some things to note: If the player is on top of multiple scrolling sectors at once, the effects add up. This causes some funky acceleration and deceleration near the door, which you can't really avoid without having one long contiguous sector (and therefore, no door). If the accelerative scroller behavior (action 216) feels cryptic, I recommend reading the Boom reference, using "216" as a search parameter to find the correct section. It explains how the final speed is calculated. Alternatively you could download the BOOMEDIT.wad, which has some nice examples of the different effects you can achieve in Boom format, including all the scroller stuff.

Simplest way to create ambient sounds using DeHackEd is to set a thing to spawn into a single state loop that constantly calls A_Pain, then setting the desired ambient sound as the pain sound for that thing. You can use the duration of the state to determine how often to play the sound, either to create a smooth(ish) loop or a periodically playing sound. In Boom, you can create the door as you normally would, then use "fake sector" action 242 on it to make it invisible.