Minecraft wiki entry for Add-on, associated text: Behavior Packs can modify the content of the game with the ability to change entity behaviors, loot drops, spawn rules, items, recipes, and trade tables. Behavior Packs can be used to alter existing content or even create new entities, blocks and items. Behavior packs are often used in conjunction with Resource Packs to create unique experiences that wouldn't be possible in the base game. [3]