The project is coming along nicely and most of the difficult things are now done.
The major improvement in this version is the addition of mob-data, which is a system of variables stored on mobs or players. What this means is you can assign your own variables to a mob when it spawns and use those in any further event. For example, you might want to give every 10th zombie a variable when it spawns and check for this variable when it dies. If you find it you can drop better loot.
You can also keep track of how many mobs a player has killed and reward/punish accordingly.