Doom 2, Update #3
The Pit: This level, obtained from FF12's release, didn't have any Progression items. However, it did have Infernal Plating to increase the armor of my Hellions, once I get them, an appropriate location for such an item considering that I killed many demons to get it. I also found a Never-Melt Ice for Emerald, two Stardrops and a Quality Sprinkler for Stardew, and also taught MP Rage to Goofy.
Suburbs: Also obtained from FF12's release, this level had a Heart Container for Zelda 1, two TMs (1 for Emerald and the other for LeafGreen), Aerial Dive and Magnet Burst for KH2, and a Lucky Punch for AlexEM. Only the Heart Container was Progression.
Industrial Zone, Pt. 1: Found through a portal in a block in Woohoo Hooniversity, this demon-infested city had two Progression items, the Grapple Beam for Metroid Prime and 24 REP for BRC. It also had several Useful items, including Slow Time Magic and Life2 White Magic for FFV, MP Rage for KH2, improved armor for Siege Tanks in Siege Mode, and some more Starting Vespene for my SC2. But the most heavily-guarded item here, in the center of the central fortress, was a recording of The DK Rap, a joke item for ArchipIDLE. To fully explore the Industrial Zone, I will need the level's Yellow Keycard.
The Citadel: This demonic castle, uncovered by Devalue at Floor 40 of the Stardew Valley Mines, didn't have any Progression items, but it did have a few other things for my Starcraft. First off, it had Khaydarin Amulets to increase the energy of my High Templars and Signifiers, Shaped Hulls to increase Diamondback HP, and Hunter Strain tech to allow my Banelings to jump up cliffs and leap towards enemies. Its only notable non-SC2 item was Goofy's Item Boost for KH2.
The Chasm: Obtained from ArchipIDLE, this map had the 2F Card Key for SetsunaLG, and the Proud Fang for KH2 for Progression items that are still necessary. I am sure Simba will be happy to have his teeth back. I also found another Golden Feather, and Protoss Phoenixes, neither of which unlocks anything new now, but both will make their games slightly easier. I also found Superior Warp Gates, to allow my Warp Gates to have three charges instead of one, and Lv. 1 Terran Infantry Armor. Last, I found a Deep Sea Scale for Emerald, which will be useful if AlexEM wants a Gorebyss.
The Abandoned Mines, Pt. 1: As it turns out, Hell has mines too, just like Stardew Valley. I entered a portal from the S.S. Chuckola Storage Room, and took down the demons here to find an infernal tome teaching Mining Mastery, which I sent to Stardew Valley. I also found a Progressive Dagger and Slime Egg-Press here for SV. I got a few non-Progression things for KH2 as well, including a Max MP Up, Item Boost, and Donald Blizzard Boost. I found a Moon Stone in these mines too, and sent it to Emerald, and finally found Nexus Overcharge tech to give my Nexuses an attack. There's one room I can't enter, and I'll need this level's Blue Keycard for it.
The Living End: Arcaneum found this level in Route 9, when they defeated Bug Catcher Connor and learned of the location of a Hell portal on this route. This had some useful treasure, but not much Progression. The only thing here that might unlock a check is the Rumbling Rose keychain for KH2, and I also found Item Slot Up and a Dark Anklet for that game. I also found some Protoss Sentries here, and the infernal powers of Hell allowed my Zerg Corruptors (when I get them) to use the Corruption ability to make targeted units take more damage. Finally, I found 18000 Gil for FFV.
I am now BKed in Doom 2.