Tlalak

Tlalak is a planet with vast oceans and land covered in lush tropical jungle. The native Tlalakans dwell in a city beneath the sea, probably because the Decepticons have taken over their old city on the land. Within a cavern on that world exists the Well of Transformation, a pool of water that can transform sentient beings between different forms.

The Transformers cartoon
The Decepticons conquered Tlalak during the Third Cybertronian War, placing the planet in the care of a drone named Deceptitran, who used an army of robotic drones to keep the population under his heel. All was well, and the slaves toiled to produce energon for the Decepticons for many generations, but finally a rebellion rose up and a large number of the prisoners escaped. Deceptitran's distress call brought a party of Autobots to the planet, in addition to Megatron and a small number of Decepticons.

The Autobots fell in with the Tlalakan resistance, and one of them, Seaspray, was even able to use the Well of Transformation to go native. With the help of the newcomers, the Tlalakans succeeded in reprogramming Deceptitran and driving the Decepticons from the planet, though the old city was destroyed in an energon explosion in the process.

The AllSpark Almanac
Tlalak is part of the Quintesson Pan Galactic Co-Prosperity Sphere.