Bjorn Hermans and Holger Nathrath cranked out three Doom episodes early in the Doom community's history, known commonly as the Serenity trilogy. Afterward, they had two Doom II projects in progress that were never completed, Serenity For Doom II and Serenity IV. Whether the latter was to be a megaWAD or just an episode, we'll never know, but we do have a few levels that were originally designed for Serenity IV but were released independently following its death. Trydent, a MAP01 replacement published in 1995, is one such offering. As with Arachna, Hermans and Nathrath's duties are switched; here, Hermans is the mapper and Nathrath his playtester.
The plot offers more of a setting than the Serenity series, but is still pretty bare as far as Doom PWAD framing narratives. You're a prisoner - though you don't know who's locked you up - and you're being held in some sort of pitch black but sensically gruesome dungeon, bringing to mind The Pit and the Pendulum. Your jailors have neglected the soundness of the cell's construction, though, and they've left a hole in the wall where the blood on the floor drains through. While you can only guess at the terrors that lie beyond, it's got to be better than the dangling company and ankle-deep blood of your current confines.
Unsurprisingly, Trydent has a heavy trident motif, with a titular silhouette cast on the floor in the first fighting room and the layout itself in the form of a trident with three separate branches pointing North. In order to clear the level, you need to visit both outer branches, after which you'll be able to access the exit switch. You start off in a fairly promising pool of blood that dumps into a greene marble room with monsters on either side. It's a neat introduction to the level that also displays a super shotgun tantalizingly out of reach. Past the door lies the main chamber, which contains Trydent's three prongs. The left and right segments have an interesting look as only the edge of each chamber is illuminated, creating a silhouette effect when viewing monsters against the lighted background, a technique Hermans would use to much greater effect in STRAIN's MAP28.
The western prong has a catwalk whose pit quickly rises to floor level (a godsend given the bullet Hell you would have had to endure to get to the other side) with a switch that assembles itself in a novel fashion. The winding path left by the zig-zag catwalk brings to mind Serenity's E1M1, if bereft of any damaging potential. The eastern leg in contrast seems pretty low key, with a crenellated wall at its end. In the name of fun, Hermans converts the cleared out end of the prong into a bunker which you must defend as monster closets open and some Hellspawn boil forth to do battle. Just don't cook yourself with the rocket.
If you're wondering how to get to the SSG, there's a secret key accessible from one of the prongs via a teleporter. The key is visible from the level's normal playing area and the secret door is quite obvious, though it's been somewhat tucked away. This opens up the red door found earlier in the level and, after a battle through a blood tunnel (where the blood from the opening dungeon cell drains to), you can claim your prize. If you're anything like me, though, you'll have cleared the vast majority of the level, making the combat shotgun of dubious importance. It might be pretty important in the context of a Serenity IV episode / megaWAD, though, given that Bjorn and Holger were demonstrably proponents of continuous play.
Trydent is a short, fun level, very much in the spirit of a megaWAD opener, and it even carries Serenity's interesting music direction. Like I've mentioned elsewhere, it's a shame that Hermans and Nathrath never finished out their Serenity IV adventure. Between Arachna and Trydent, it's clear that Bjorn swung hits as a mapper. Trydent may not be the most challenging Doom II you'll ever play, but if you're looking for a romp, this one ought to do.