7 Days to Die Wiki
Some items' or groups' chance to drop changes according to the player's gamestage. Here you can see those values for any gamestage you want using the little box below. Just type the gamestage you want in the box and press the Apply!-button. The values should change immediately, if the chance is different.

Current game stage: 1

Starting in Alpha 17, 7 Days to Die has been using Unity 2018 as a framework. As such, if you are interested in adding custom assets, such as new entities, sounds and blocks, you will need Unity 2018. The following YouTube Tutorial by Xyth is a great starting point. Some additional information can be found in Unity.