In balheimr you can steal the egg to get the egg you have to go to either side of the scar and find the purple crystals and then go in and when you look an the lave you will see magmasaurs and the island in the lave is where egg are laid and when you hatch the egg feed it as much sulfur. Sulfur can be found an the wyvern statue at the top of the volcano it looks like a white rock it will be real shiny use a pickaxe to harvest it. When it is fully grown if you hold Y if you are on Xbox E if you are on PC and PlayStation the top button on the controller I do not know what it is because I only play PC and Xbox then turn on smelting and if you put something smeltable in the magmasuarir will smelt