We shall begin this episode by talking about what it is not. The 4th Encounter, then, was a modification of the Macintosh Second Encounter Wolfenstein 3D engine created by one Greg Ewing, who is also the author of WolfEdit, the definitive Mac Wolf scenario editor. It must be said that the default mode of editing and distributing Mac mods was suboptimal in certain regards. New art was stuck inside the scenario file's resource fork, compressed. Well, things like the episode thumbnail were uncompressed, but that's about it. New sounds (if any) were provided in a separate file's resource fork and had to be copied over the vanilla game's sound files via ResEdit hackery. To facilitate sharing of art, sounds and music between sets of levels (that's a quote), 4th Encounter introduced a different file loading scheme: namely, it would allow one to keep their mod's art and sounds in separate files placed in appropriately named folders ("Levels", "Shapes", "Sounds" and "Music"). It also implemented a functional scenario selection feature, which the Second Encounter was missing. It should be needless to say that we are not going to port this. It would make very little sense to port a game engine fork developed to solve problems not relevant to PC versions and their modding scene.
And yet, you're getting not one, not two, but three "4th Encounters" in this update. Well, sort of. You'll see in a bit.
For as it turns out, calling something a fourth encounter (coming after the initial three) seemed like a good idea to more than one person. One of those other people was Clubey. His 4th Encounter is a 10-floor First Encounter mapset that received its name at least partially because it was also the fourth complete scenario created and released by Clubey. The readme talks about brushing up editing skills etc, but you'll already be seeing some rather familiar map features, specifically all the cramped spaces, extremely high enemy numbers and density, or crossfires you have to get out of, and fast. The documentation also mentions a "death version", though I actually don't know if this version is the death one, or where to acquire it if not. But I shudder at the thought of something even more packed with Nazis!
The other two 4th Encounters are closely related, though the exact nature of their relationship is a bit uncertain because of course there's no documentation attached. All I know is that there's a 10-level First Encounter version released in 1995, and a somewhat edited, smaller (!) 8-level Second Encounter version dated 1997. I'll be blunt, the maps are very simplistic, oddly decorated, and there isn't even much to fight, at least in the 1st Enc. version, because the 2nd Enc. one throws some Encounter-specific bosses into the fray, multiple ones per map. These go well along with all the ammo... or lack of ammo, as the case may be, as unfortunately at least one map when there's barely anything to pick up still has you face a boss (who can technically be evaded, but then you can kiss your 100% ratios goodbye). Oh well, go check them out yourself and see if this is your kind of entertainment.
But wait, there's more! Still centered around the number 4 too. I'm sure you're delighted if you're into numerology or other pathetic attempts at finding order where there's none. Either way, our next scenario probably should have been called The Fourth Reich, but is actually named The Forth Reich, so that's how I'm distributing it. Either way, Clubey delivers another 15 maps for the First Encounter, although by his own admission, some of them are borrowed from other mapsets and probably modified to fit. True to this description, there are clear differences in style (and size) between many of those maps, so the whole thing is a bit of a potpourri, but you can identify some hallmark Clubey stuff if that's what you're after. Not that I'm willing to make any bets.
So... 4 mods in a release centered around the number four. Perfect, right? Yeah, no. Here's a fifth one. Consider your day ruined. The mod's called Four Quality Levels and it offers four quality levels for the First Encounter. Your mileage may vary. They are certainly extensive though, so you get a lot of bang for your buck. Mild in difficulty (plenty of brown guards, but also with a boss on every map) and fairly rectangular otherwise.