To separate a mixture of hard candies and marbles, the most efficient method would be

If the marbles are stuck in the candies you boil the candies until they melt but do it in water then put a strainer in the sink and run cold water 2minutes befoer and after dumping it into the strainerand while dumping it so you do not ruin the water pipes

I think hand picking is best for this case. another method can be done in which first u have melt those candies with marbles. u will hart candy will melt quickly. so, when candies melt, u will find marbles are still solid but candies are in liquid form. now take a net and purify that solution (candies and marbles). now the candies will pass through net but marbles will stuck in upper net. remove marbles now