Set in the 29th Century, the story starts with a Galactic Conqueror and God of Evil and Destruction known as BIOS, who has created eight evil gods and gone on conquering and destroying worlds, turning them into husks of their former selves. Eventually, Earth is targeted and suffers the same fate, becoming a barren wasteland known as the "Dust World". The few humans that have survived decide to fight back by raising and training two boys into badass super soldiers. This works wonders, and the two now adult Nameless Soldiers embark on a quest to defeat BIOS.
The game was quite successful back then, getting ported to many consoles and home computers of the time, including the Sega Genesis (which had to cut a few things, like voiceovers and two stages) and later the TurboGrafx-CD (which removed two-player co-op, but included a bunch of bonus features). The main characters were also brought back somewhat reguarly in several of the company's Crossover games.
This game provides examples of:
- Ancient Egypt: The setting of Stages 4 through 6, the Pyramid World.
- Arms Dealer: Sylphie.
- Asteroids Monster: Some enemies in later stages.
- Background Boss: Stage 3 boss, War God.
- Big Bad: BIOS, King of Gods.
- "Blind Idiot" Translation:
- The ending has some humorous examples.
Sylphie: Thank you very mach.
Now peace is retvrning to this town again.
We'll rebuild this town no matter how long it takes.- Raijin and Fujin (Stage 8 bosses) were mangled into Laidin and Whodin.
- Captain Ersatz: Laidin and Whodin resemble Raiga and Fuga from Fist of the North Star.
- The Cameo: Both Unknown Soldiers appear in Ken's stage in Street Fighter Alpha 2 as guests, and they also appear in the Mega Man (Archie Comics) series.
- Color-Coded Multiplayer: Player 1 in blue and Player 2 in red. However, their sprites are not only different (Player 2 wears a tank top and has a mohawk hair style), their weapons are as well. Player 1 uses a long-range automatic rifle, while Player 2 wields a short-range wide shot.
- Crossover: "Unknown Soldier 1P" appears as a challenger in the quiz game Adventure Quiz: Capcom World and its sequel. Sylphie and the Dust Dragon appear in the sequel as well, the former as the "INN attendant" and the latter as one of the three dragon bosses.
- Capcom vs.: Unknown Soldier 1P is one of several Assist Characters selectable in Marvel vs. Capcom: Clash of the Superheroes. One stage also has background cameos of bosses Raijin & Fujin as well as Final Boss BIOS. Both soldiers and Sylphie make the jump to playable characters in Namco × Capcom. Finally, Sylphie makes the jump in Project × Zone 2: Brave New World but only as a NPC.
- Crapsack World: Earth is a wasteland ruled by a cult of reptilian humanoids and humanity is almost extinct.
- Divergent Character Evolution: Inverted in the Genesis port. Player 2 had a different shooting style in the original arcade version, in which he had a short-range wide shot in contrast to Player 1's long-range single shot. In the Genesis version, he operates exactly like Player 1 does.
- Dracolich: The Dust Dragon at the end of the second stage, a dying rotten dragon with its stomach open and its innards and ribs exposed.
- Dual Boss: Raijin & Fujin, a literal Red Oni, Blue Oni (they're Onis with that colour!). They take turns attacking you from the sides, and swaps around occasionally, although you only need to really concentrate on attacking one due to their Shared Life-Meter.
- Dub Name Change: The Sega Genesis manual changed Sylphie's name to Mirabella. It also changed the names of the War God and Bios into Iron Warlod and War Tyrant, respectively.
- Dungeon Shop: One has to wonder how Sylphie was able to set up a shop that magically rises from beneath the ground just as the soldiers come by...
- Enemy Summoner: The Dust Dragon generates Reptilian Mooks from his mouth.
- Eternal Engine: The first stage eventually gets into one of these, with giant gears and pipes that release a blast of fire when shot.
- Evil Tower of Ominousness: The Tower of Babel (a.k.a. BIOS' lair) seen in the background of the Raijin and Fujin Boss Fight. The final stage scrolls upwards instead of sideways, as the soldiers ascend through the Tower of Babel.
- Expy: Two P. from Final Fight was modeled after the Player 2 character of this game. Even Two P.'s name is a reference to him (Two P.= 2P).
- Several to Fist of the North Star: War God looks like a gigantic version of Raoh, while Fujin and Raijin resemble Fuga and Raiga.
- Fantasy Kitchen Sink: Among the evil gods we have representatives from Classical Mythology (War God), Egyptian Mythology (God Rah/Mesketit and the Sphynx) and Japanese Mythology (Fujin & Raijin). And then there are the giant dragons, humanoid reptile cultists, floating martial artists, ice monsters, humongous undead buddhist monks...and cyborg Tutankamen.
- Flight: The Unknown Soldiers and several human Mooks fly throughout the game. In the former's case, thanks to gravity equipment.
- Galactic Conqueror: Emperor Bios goes across the galaxy, conquering and turning entire worlds into ruined wastelands to be ruled by his subordinate gods.
- Good Old Fisticuffs: The huge War God throws some heavy punches at the player during the boss fight.
- Homing Projectile: Homing Missiles and Homing Lasers are among the Satellites to purchase.
- An Ice Person: Iceman, Stage 7 boss.
- Ki Manipulation: Martial artist-esque Mooks attack with this.
- Level in the Clouds: The Sky World (stages 6-7) has the player make their way across a cloudy landscape scratched by frozen elephants, dragon sculptures and tall buildings. There's also a brief part that shows a cherry blossom forest above the clouds.
- Lizard Folk: The Reptilian Thugs, early stage Mooks and religious followers of the War God.
- Macross Missile Massacre: Not actually missiles, but BIOS has one attack in which he sends a shower of difficult-as-hell-to-avoid homing lasers upon the player.
- Market-Based Title: While the original arcade game was titled Lost Worlds in Japan, all the console ports (including the version in Capcom Classics Collection) were titled Forgotten Worlds in Japan, presumably due to trademark issues.
- Mind over Matter: The main power of the first boss, Paramecium.
- More Dakka: It is a SHMUP, after all. The default weapon given to the soldiers in all their cameos is the machine gun.
- Multi-Armed and Dangerous: BIOS sports six arms.
- The Nameless: Both player characters are only known as the "Nameless Ones". This is kept in their cameo appearances, usually going by the monicker of "Unknown Soldier" followed by 1P/2P to identify between them. The Japanese sources have slight variations at times, like "Nameless Super Soldier". The MegaDrive Japanese manual also refers to the 2P soldier as "Mohawk Man".
- Orcus on His Throne: When the player reaches BIOS's chamber, he's nonchalantly sitting on his throne.
- Our Dragons Are Different: The War God is shown using several western-styled dragons in the intro. One serves as the boss of Stage 2, named the Dust Dragon, which for some reason is half-beaten and missing some patches of flesh (including the whole stomach).
- Physical God: BIOS, the Big Bad, is capable of creating god-like entities by himself.
- Pinball Projectile: The Bound satellite.
- Powered Armor: Player 1 starts battle shirtless, while Player 2 wears a dark blue tank top, and get their more iconic armored look after picking up armor upgrades which provide limited protection (from three or five hits, depending on whether it's the weaker or stronger armor).
- Press Start to Game Over: In the Genesis version, upon starting the game with a 6-button controller connected on either controller port (when the MODE button is not held upon startup) would trigger a Game-Breaking Bug to instantly get a game over (also when a 6-button controller is plugged in during gameplay).
- Segmented Serpent: Worms in Stage 2, dragons in Stage 7/8 and the boss of Stage 5, Centipede.
- Shock and Awe: Raijin and Fujin conduct electricity between them as one of their attacks.
- Shout-Out: There's an amusement park in the story mode of SNK vs. Capcom: Card Fighters Clash, which is filled with references to the game: It's named "Lost World", its theme music is from the game's first stage, several in-game weapons are exhibited and Sylphie herself appears as a card seller.
- The alt color for the Unknown Soldier in Marvel vs. Capcom: Clash of the Superheroes is one to his 2P buddy.
- The stage 2 boss, the Dust Dragon, has a weak spot with his heart. Capcom released another game 24 years later that has various dragon enemies with their hearts as weak spots.
- Shows Damage: Some bosses, like the War God and Dust Dragon, visibly break apart as the battle goes on.
- Videogame Flamethrowers Suck: The Burner satellite.
- Walking Shirtless Scene: Player 1 without the armor pickup (Player 2 has a dark blue tank top), and second-to-last bosses Raijin & Fujin.
- Wave-Motion Gun: There are 3 different laser weapons in the game, even the weakest of these packs greater firepower than most other weapons, with the deadliest and most expensive of these being the Homing Laser
- Winged Humanoid: BIOS.
- Good Wings, Evil Wings: Subverted. The very evil BIOS has...white featherly wings.
- Your Head Asplode: Raijin and Fujin blows their craniums once they're down.
