The Everfree Forest is first introduced in Friendship is Magic, part 2, when Twilight Sparkle reads the book The Elements of Harmony: A Reference Guide. It specifies that the Elements of Harmony's last known location is in the ancient castle of the royal pony sisters, and that the castle itself is located on what is now known as the Everfree Forest. Twilight Sparkle and her friends enter the forest in order to retrieve the Elements.
When the ponies venture for the first time into the forest, Applejack mentions that "It ain't natural, folks say it don't work the same as Equestria". Fluttershy, Applejack, and Rainbow Dash surmise in Bridle Gossip that the forest "just ain't natural"; the plants grow on their own, animals take care of themselves, and clouds move without pony intervention.Fluttershy, who lives in a cottage near the edge of the forest, tells the Cutie Mark Crusaders in Stare Master that the forest is "much too dangerous" and is "filled with far too many strange creatures". These include timberwolves, the manticore, a notable sea serpent, Ursas, parasprites, dragons, and the cockatrice. Timberwolves are shown in both Family Appreciation Day and Spike at Your Service, while the rest are respectively featured in Friendship is Magic, part 2, Boast Busters, Swarm of the Century, Owl's Well That Ends Well and Stare Master. The abundance of monsters explains why the ponies are wary of the fact that Zecora makes her home in the Everfree Forest, citing it as one of the reasons they fear her in Bridle Gossip.
The forest is mentioned more than once as a place of banishment. When Rainbow Dash panics over her impending performance in Sonic Rainboom, she fears that she will be banished into the Everfree Forest for her failure. Similarly, in A Bird in the Hoof, Twilight suggests that she and Fluttershy will be banished and possibly imprisoned in the Everfree Forest for kidnapping Princess Celestia's pet phoenix, Philomena.
The Everfree Forest also contains many types of flowers, poison joke being among them. In Bridle Gossip, Zecora cures Twilight Sparkle and her friends by using medicinal plants.In the episode Too Many Pinkie Pies, Pinkie Pie ventures into the Everfree Forest to look for a magical pond that she recalls from a nursery rhyme. She pushes through dense brambles and unexpectedly falls down a hole, but ends up in an underground cavern that houses the Mirror Pond. She recites, "And into her own reflection she stared, yearning for one whose reflection she shared, and solemnly sweared not to be scared, at the prospect of being doubly mared!" and steps through the surface of the pool, successfully cloning herself. This process continues until there are a sizable number of clones, who start overwhelming Pinkie's friends. When all the clones are sent back, Twilight seals the entrance to the mirror pool with a boulder.
According to one of the comics in the German magazine, a land outside of Equestria lies beyond the Everfree Forest.