The Shadow Forest is a scary forest that actively tries to kill anything that tries to travel through. The spooky trees can generate spears to impale a traveller with or just attempt to crush them to death.
In My Little Pony: The Movie, a group of Ponies and the Williams kids only make it through the Shadow Forest thanks to a Twinkle Eyed Unicorn named Fizzy's bravery as she breaks off and attracts the trees' fire so the others get away. After dodging the projectiles through skillful use of a teleportation spell she manages to barely escape herself.
The Shadow Forest may be the precursor to the Everfree Forest from My Little Pony: Friendship is Magic. One scene even has trees with monstrous faces created by Nightmare Moon's magic.