Troll

Trolls are mythical, magical creatures who live adjacent to the Enchanted Realm/Kingdom. They can be seen in Tween places such as windows and doorways, even shadows. They come into existance in our realm at midnight, when the thin veil between our realm and the Enchanted Realm lifts. They can either be good or evil.

Trolls are mischievous, very fast, sneaky, vile little creatures who will do anything for a chance to rule the Enchanted Kingdom; they are related to Gremlins. Don't be fooled, although very small, they are strong and cunning.

An evil Troll's respective enemies are Fairies and other good magical beings who dwell within the Enchanted Kingdom.

Trolls appeared in the episode Once Upon A Time, holding Fairies captive and kidnapping a girl, Kate, to steal a Fairy named Thistle that she was protecting. A few of them were vanquished by The Charmed Ones who could see them after being sprinkled with Fairy dust, and casting a spell cultivating innocence. They also appeared in Something Wicca This Way Goes attacking Zankou when he tries to gain control of the nexus, making him trip down the steps.

Giant Trolls
In Show Ghouls, a troll visited Magic School during Drake dè Mons class of Magical musical compositions. The troll had taken all students from the ground, dancing around on '20s music. Giant trolls are presumably neutral or good beings, as they could enter Magic School. Giant Trolls are obviously harmful to some beings, but being that they could walk into Magic School makes it seem that they would not harm a good being.