Mild references primarily. In one episode the outline of a nude woman is shown drawn on a wall.
Violence & Gore
Mild
Some episodes involve myths about weapons, usually guns.
Sometimes they will add fake blood to dummies and in some episodes animal blood is shown. Occasionally, people are hurt.
Profanity
Mild
Several mild languages such as "damn," "hell," "crap," etc. Some uses of "pissed".
In some TV-14-rated episodes, "ass" is uncensored. However, more serious curse words are bleeped out.
Many, many uses of "God" and maybe at least one "Jesus". Anything stronger than the show's ratings are bleeped.
Alcohol, Drugs & Smoking
Mild
In one episode, one of the main characters drink up to the legal limit of alcohol and then drives a car. Police are nearby and ready to help though.
One episode in the early seasons features the two main hosts getting drunk on camera to test whether various techniques would work to foil a breathalyzer test.
Frightening & Intense Scenes
None
Some of the myths they test involve the use of real human skeletons and animal carcasses, which may make some viewers squeamish.
When bombs are about to be blown up, or people do scary things.