Ground Poppy Dust

Ground Poppy Dust is a magical item featured on ABC's Once Upon a Time. It first appears in the sixth episode of the second season.

History
Emma Swan, Mary Margaret, Aurora, Mulan, and 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.
 * -|After Broken Curse=

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. Later on, Emma convinces the Giant to give her the compass while also bargaining for a favor to keep Hook, who is not trustworthy, trapped while she makes her way down the beanstalk.

After Aurora is abducted by Cora's undead army, Mary Margaret and Emma no longer have a way to communicate between worlds. Since 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 flower, crushes it into dust and blows the substance towards Mary Margaret, who promptly falls asleep.

Through a journey to rescue a kidnapped Henry, David, Emma, Hook, Mary Margaret and Regina work together to maneuver the jungles of Neverland. Using a map from Pan, they track the changing location of his camp. Hoping to receive help in getting to Pan, Hook suggests they look for Tinker Bell. Regina begins to lag behind as Emma also stops to inquire about the nature of her connection to Tinker Bell. Refusing to elaborate, Regina simply puts it as a "complicated relationship" and urges Emma to go on ahead while she stays behind. Left alone, Tinker Bell creeps out of the brush to confront Regina about what she overheard her say just moments before. Still harboring animosity over their past, Tinker Bell blows poppy dust from her palm into her nemesis's face; causing Regina to collapse unconscious.

Trivia

 * In the novel, The Wonderful Wizard of Oz, poppies cause people to fall asleep.
 * Poppies are rare in the Enchanted Forest so Mulan had to travel to another kingdom to find one.