Terrigen Mist

"Break the crystals and release the Mist; either they're Inhuman or they're dead."

- Jiaying

The Terrigen Mist is a gaseous substance that is produced by Terrigen Crystals. When an Inhuman is exposed to the Mist, they generate a rocky cocoon and undergo Terrigenesis, developing superhuman powers.

History
When the Diviner opened to reveal the Terrigen Crystals inside, the Terrigen Mist filled the temple of the Kree City and surrounded Raina, Skye, and Antoine Triplett, who watched as the women were seemingly petrified upon exposure to the Mist. Triplett kicked the crystals, causing them to shatter. When the Mist cleared, Skye shattered her cocoon along with Raina.

Appearances
In chronological order:
 * Agents of S.H.I.E.L.D.
 * Season Two
 * Aftershocks (mentioned in a flashback)
 * What They Become
 * One of Us (mentioned)
 * One Door Closes (mentioned)
 * Afterlife (mentioned)
 * Melinda (mentioned)
 * Scars
 * S.O.S. Part Two

Trivia

 * The mist doesn't just trigger Inhuman superpowers; in Raina's and Gordon's case it caused their body to change physically.