Player can complete mission consisting of returning items for certain npc. There is a in game window with all important information. On administrator side on things, you can add as many missions as you wish, for unlimited npc. Configuration file is easy to use and also tutorial is provided.
First, when you open the window there is list with all ongoing missions.
Then you have all the information about selected mission, basically, what you return, chance, time you have to wait in order to return next item, amount of returned items / amount required, mission level, map where you drop item and render of each mob, list of rewards. Player can choose between returning one item a time or all at once. In second case, time is multiplied by number of items returned. As you can see, there are two slots, one is just required item, second is elixir which increases chance. By clicking LMB you change it between two different elixirs, RMB activates one of them.