Oh my. Normally I’d happily greet you and welcome you to the forum, so pardon that I don’t do that now. While there are several things that could be the problem, because of the malformation of his casque, I’m guessing he hasn’t been getting proper supplements or uvb light. That leg has some dark discoloration like a bruise, so it could possibly be a bone fracture. Do you by chance have any information as to the care that he received before…type of supplements, lights, diet, etc? We can help you get his husbandry correct, but I think the best thing to do right now is to get him to a good vet experienced with chameleons as soon as possible. An x ray will be able to show what is going on with his leg(s), his general bone density and several other things that could be a problem. Blood work would show his organ function, calcium levels and such. If you can get a fresh poo, a fecal test for parasites is always a good idea too.