Interesting, my $0.02:<p>Initially some of the drops are specified using percentages. My advice is to never use percentages when selecting chances to pick an item from an arbitrary list of items. Instead, use numbers which loosely correlate to ratios. Here is an example list of items:<p>1, 1, 2, 2<p>the chance of picking the first item is 1/(1+1+2+2) or 1:6. The chance of picking the last item is 2:6. Using this method, you can add arbitrary odds to the list and it will automatically total up the odds for you. For example:<p>1, 1, 2, 2, 3<p>The first is a 1:9 chance, the last is a 3:9 chance. The numbers still maintain relative chance next to one another - i.e. you are 3 times more likely to get the last item than the first.<p>This is better than using percentages because you can add items without having to recalculate the percentages so that everything adds up to one hundred percent (yes you could normalize the percentage but this still makes it tougher to understand the chance of each item relative to one another. If you want to make a high chance of dropping nothing, simply add a null item to the list with a really high chance, i.e.:<p>(null) 99, (diamond) 1<p>This results in a 99/100 chance of dropping nothing, and a 1/100 chance of dropping a diamond.