World-Turtle

In the vast dark void of space they swim. Ancient chelonian hearts burning like stars against the cold of the deep. On their backs they carry a multitude of worlds, each vibrant and unique. These are the World-Turtles. It is unclear whether World-Turtles are the creation of some incredibly ancient cosmic Deity or perhaps the original inhabitants of The Astral Sea itself, still, the world-turtles are found in the earliest records of the gods themselves and in the art and legends of every mortal civilization which has ever existed.
World-Turtles are vast arcanophages, magic eaters who absorb raw magic stuff into their bodies to sustain their impossible existence. With this huge arcane resevoir they are able to sustain habitable biomes atop their shells, even in the violent swirling energies of the Astral Sea or the depths of space. This symiotic relationship provides mortal beings with a safe and stable home and in exchange they exude a kind of ambient psychic energy which helps the World-Turtle to grow.
The largest World-Turtles recorded by the more observant gods and arcanists are as large as planets, sustaining a whole complex of seas and continents, even holding miniatures stars and moons in their orbit. It isn't clear how World-Turtles mate or whether their reproduction is even sexual at all. World-Turtle eggs are incredibly rare treasures with a magic density greater than any known material. Thankfully the eggs are also nigh-impenetrable, making them a poor target for thieves. The eggs are laid in singular clutches, a single egg the size of a cart, deposited on a lively and thriving world. After laying dormant for centuries, the egg hatches and the newborn turtle begins swimming through the native oceans of the world, accumulating its first life forms. With each life form the turtle grows and increases, becoming larger and more powerful. When they reach the size of a small continent they leave their birth worlds behind and make for the depths of space according to some unknown homing instinct.
Mature World-Turtles have a macro-intelligence comparable to a grand deity though they rarely feel the need to communicate directly. Because of their indestructible hides, World-Turtles are almost impossible to threaten or harm. Against the few foes that merit their caution World-Turtles can unleash rays of pure solar light from their mouths or local suns. These beams are capable of destroying any and every material, species and even divinity which has yet been discovered.