This page alone will demonstrate just how dark and scary Captain Scarlet is compared to Thunderbirds.
- The idea of getting brutally murdered and getting replaced by an alien copy without anybody knowing is a bit scary.
- Potentially taken further with Scarlet; it's never analysed in depth, but according to all evidence, technically the 'original' Scarlet died in the pilot episode, so the one the series focuses on is 'just' a duplicate with all of his memories who nevertheless isn't actually him...
- The inherent Paranoia Fuel is brought to the viewer's attention from the pilot. After Colonel White entrusts the President to Captain Scarlet, Captain Brown's body is found near the SSC crash site, alerting White to the fact the post-crash Captain Brown was an impostor. Then Lieutenant Green points out that Captain Scarlet was caught in the same crash... and White, realising what has likely happened to Scarlet, promptly orders Green to contact Destiny Angel and have her escort "Scarlet" back to Cloudbase, but it's too late. "Scarlet"—who is not the original Scarlet's soul inhabiting a clone yet—refuses to acknowledge Destiny. Both the post-crash Brown and the post-crash Scarlet were Mysteron sleeper agents, and Spectrum was none the wiser until the President was in the Mysterons' clutches... and after a failed assassination attempt. The only reason Spectrum manages to save him in the end is because the truth came to light in time.
- One of the audio episodes, "Captain Scarlet is Indestructible", features the Kill and Replace from the victim's viewpoint — they get into a bath, feel themselves drifting off, then the next line is the Mysterons informing them there was a fast-acting poison in the bathwater and they have been reborn under Mysteron control.
- The whole "Attack on Cloudbase" Episode if you discount the ending.
- Any scene with Captain Black... good God... the guy's Nightmare Fuel incarnate.
- How about the artwork in the end credits? Seeing the hero about to be crushed by closing spiked walls, tied up and sinking while sharks close in for the kill...
- Better still because we're used to these as James Bond death traps where the hero somehow escapes. Here, the full implication is that Captain Scarlet doesn't escape. He dies, painfully, and respawns.
- It's surprising that the kids of the 60's who watched this weren't scarred for life at the death toll. At least 6 people die per episode — people EXPLODE, fall out of airplanes, fall off dams, get crushed by car lifts, get run over, get shot in the FACE, and turn into living bombs.
- The opening credits put the camera in the viewpoint of someone sneaking down a dark alley who is suddenly caught by searchlights, unloads an entire clip into his attacker and is shot dead. By the Hero, who doesn't even flinch as he does so.
- In almost every episode, at least one person is killed so they can be replaced by a Mysteron "clone". Crushed in garage car-lifts (while cheery music (turned up loud, no less) plays from the garage radio), strangled with robot hands, brake lines cut. And then we see the dead body duplicated by the Mysterons. For true nightmare fuel, watch the end-credit sequences, where Captain Scarlet is subjected to ten different death-traps.
- It gets worse when Fridge Horror kicks in- he still feels pain. Not only that, but he may never die, meaning he's doomed to watch everyone he ever cared about wither away, until he is alone.
- The Mysterons themselves are Nothing Is Scarier incarnate. All that is ever shown of them are the two infamous green rings and the iconic booming Hell Is That Noise voice. They'd be unsettling even if they weren't trying to Kill and Replace humanity.
- "THIS IS THE VOICE OF THE MYSTERONS. WE KNOW THAT YOU CAN HEAR US, EARTH MEN."
