World War I/Nightmare Fuel


 * Poison gas. Worse, every side wound up using it at one point or another, and each flavor that proved popular brought its own flavor of horror.
 * Initially, chlorine gas was the first general type. On top of it looking like poison (it was a yellow-green cloud generally that was heavier than air and thus seeped into the trenches with disturbing ease), it killed by essentially causing a person to drown due to it essentially crowding out all the room in the lungs so no oxygen could get in.
 * Phosgene was the next oft-used gas. Creepily enough, it actually smelled pleasant, like new-mown hay. You could even breathe it in initially with no ill effects. Then, several hours later, it would break down into the lungs as hydrochloric acid, meaning it literally killed its victims by melting their lung tissues, causing a painful death.
 * Chloropicrin, also called "vomiting gas", wasn't too bad by itself aside from being weaponized Nausea Fuel. The scary part is that it was designed to break past most gas masks, and when the victim tore off their mask to throw up, they'd inhale the even worse agents like phosgene.
 * The worst of all was mustard gas. In small concentrations, the far off scent wasn't too horrible, but up close it was sheer agony. In fact, it was not so much a gas as an atomized liquid, meaning that it quickly turned into a liquid form that adhered to surfaces for weeks at a time. On top being phosgene except for the whole body (which could blind people, cause permanent lung damage like Adolf Hitler's infamous barking tone to his speech due to throat injuries, and otherwise was a general burning acid agent that caused previous skin issues), it made the trenches the worst spot you could ever be in until it wore off, because it remained active for weeks on end, and unless the trench was completely cleansed with agents like powdered bleach, that meant the trench itself was killing you even if you could avoid getting shot by slow poisoning.