Most of the wildlife in the Forest of Tranquility is sociable and fairly benign to visitors—in fact, the main threat one faces in the forest is the possibility of having too much fun to ever leave.
During their hunt for the Golden Weapons, the Ninja and Master Wu landed in the Forest of Tranquility after using Mechanical Wings to escape from the Floating Ruins. The group set up camp for the night in the forest, but Kai was tricked into going to the Fire Temple by Lord Garmadon. After Master Wu followed his wayward student, the other three Ninja were attacked by Samukai's Skulkin forces, who managed to steal the three Golden Weapons the Ninja had collected.
After the Ninja had defeated Lloyd and Hypnobrai tribe, Lloyd has begun to build a big and dangerous tree house in center of the forest. Zane, with little help from Falcon, found it, told other Ninja, and they destroyed Lloyd's tree house.
After being exiled from the Hypnobrai Tomb by Hypnobrai General Skales, Lloyd Garmadon decided to release another tribe of Serpentine to combat his former allies. To this end, Lloyd followed the Map of Dens to the depths of the Forest of Tranquility, where he discovered the Fangpyre Tomb and unleashed the snakes within.
During the Ninjas' hunt for Samurai X, Kai encountered a trio of Constrictai in the Forest of Tranquility. Cheered on by a trio of fangirls, the Red Ninja prepared to battle the snakes, only for Samurai X to arrive and incapacitate the Constrictai in seconds. Angered by the intervention (as well as the fangirls' fawning over Samurai X), Kai attempted to attack the Samurai Mech with Spinjitzu, ending up trapped in another net for his troubles.
After Pythor released The Great Devourer, the Serpentine fled to the Fangpyre Tomb when it became clear that they could not control the monstrous beast. The last of the snakes had barely finished jumping in and sealing the tomb when the Devourer slithered through the forest, knocking over many trees but ignoring the Fangpyre Tomb.
In the past, after having kidnapped Nya, the Ninja set off to deliver her to the Skeletons in the forest.
After being chased by Morro, the Destiny's Bounty crashed in the Forest of Tranquility. The Ninja set up a campfire there and spent the night until Misako arrived the next morning to translate the three symbols on Wu's staff. The Ninja then mounted on Wallipers to head to Stiix while Nya, Wu, and Misako departed in the Destiny's Bounty.
Following his battle with Lloyd in the Corridor of Elders, Pythor ran to the forest of tranquility.