Fear Gas

Fear Gas, also known as Fear Toxin, is the signature weapon used by the Scarecrow. Coming in a variety of forms (gas, liquid, powder) the substance induces involuntary and sometimes irrational fear in a victims' mind. Depending on the dosage amount and amount of time infected the gas has the ability to psychologically break the victim's mind; driving them insane.

A versatile substance, Fear Gas can be delivered through a variety of means through gas, darts, capsules, etc. His mask was made in order to enhance the effects of the hallucinogen while also acting as a gas mask to keep from poisoning himself.

Trivia

 * As he is with most chemicals, the Joker is immune to Scarecrow's Fear Gas.