Ground Poppy Dust

Ground Poppy Dusthas the power to put people to sleep.

History
Emma Swan, Mary Margaret, Princess Aurora, Mulan, and Captain Hook were in search of a beanstalk which would lead to the home of a giant. The Giant was in possession of a magic compass they needed to get back to Storybrooke. Emma decides to climb the beanstalk with Hook, and just before she goes, Mulan gives her a small bag of poppy dust to use on the giant.

Hook draws the giant out of its lair and lures him to Emma's side where she throws the dust. The Giant is knocked out instantaneously, and the both of them go inside to look for the compass. ("Tallahassee")

After Aurora is abducted, Mary Margaret and Emma no longer have a way to communicate between worlds. Because Mary Margaret has already been under a sleeping curse, she can contact Henry if she falls into a deep enough sleep. Mulan takes them to a nearby kingdom where she finds a poppy and crushes it into poppy dust. After she tosses it into Mary Margaret's face she falls into a deep slumber. ("Into the Deep")

Trivia

 * In the novel The Wonderful Wizard of Oz, poppies cause people to fall asleep.
 * It is made by Mulan who crushes the poppies into dust with her blade.
 * Poppies are rare in Fairytale Land, so Mulan had to travel to another kingdom to find a poppy. ("Into the Deep")