My creature, called the Kurbish, inhabits a wasteland-world, in my universe.
Recently, I have been wondering; "How plausible is this thing, really?"
A description: Large, Elephant-like creatures that photosynthesise. They feature intelligence not unlike Humans. They grow a number of precious minerals in the crevices in their shell-like back, along the length of the spine.They can grow to be 125 feet tall, and can be up to 3 kilometers in length. They don’t have to traditionally eat, but they can eat and digest several types of rock and metal. The crystals on their backs grow as they age, and grow in various colors and types to represent the diets and emotions of the Kurbish. They have large tails, on which very precious minerals grow. The Kurbish have anywhere from 6 to 18 legs, and are able to communicate subsonically(around the same level as a black hole). They grow crystal tusks as they age, and they are able to regenerate if damaged or destroyed. They have around 28 eyes, with around 14 being on each side of the head. They are able to have multiple heads, albeit rare for it to happen.Their shells feature microbiomes, which changes according to the emotions, health, and age of the Kurbish. These microbiomes grow and change with the Kurbish.
Aside from the sizes, which is impossible for a normal, living, creature, how plausible would this creature be?