What powers does your character have if you've though of any so far? Can he get stronger? Weaker? Or is he just set and where at if so?
Since this is fiction you can really do whatever you want or whatever the plot requires if your lazy lol.
But seriously, the reason he is a god is because there is no other explanation I could give him. He can't be a human because he is made of pure diamond and is not human. Even a character made of diamond is still not possible because you need like a brain and such to think so the character is truthfully not possible in our universe. This is why I'm calling him supernatural because it really cannot be explained using regular logic.
He is pretty darn strong. Strong enough that no human could ever win in a one on one tug-of-war match. I would say that a good tug-of-war match would be with Godzilla (the kind of monsters). I like the idea of him going into battle and loosing to a very strong opponent only to walk away and figure out a different strategy and then come back ever stronger.
Like you can lose in a match and still not get any stronger but figure out what went wrong and then come back with a different battle plan and win.
I also like the idea of him discovering new powers of his. Like for example, he has the ability to create energy blasts from his hands, but he didn't know that at first, he had to discover that he could do this.
So over time he learns more about himself and more about his own powers. As he learns new powers he thus becomes "more powerful".
Also eventually he will die of old age. Apparently diamonds degrade to graphite after so many billions of years so when he gets to be really old he will turn into pencil lead. LOL. But he can always be rejuvenated with actual diamonds and come back to life. So it makes for good story telling when you can kill a character and bring him back and such.