Well, this is a SlotMachine style NPC that I created long time ago and I didn't give him any use, so I'll share it.
How it works? First of all you can configure it via .properties file so it's easy for newbies. Then, the NPC consumes X quantity of items and X am.ount of those items for each try, when you try once, the npc starts showing you a html with 3 icons, each slot has 3 possible items, the NPC randomly change every slot X times so if you have luck and after all 3 moves all 3 icons are the same, gz you won, otherwise the items were consumed and you won nothing, try it again. As I said, feed and reward is easy configurable, same with NPC ID and with the Server Name, which will appear in the html shown by the NPC.
Have fun, here a video if u didn't understand how it works.
And yes it's done using Thread.sleep(); I know... if u don't like, rework it with ThreadPool.