Minecraft wiki entry for Music_disc_farming, associated text: When farming music discs, you want a way to make the skeleton and creeper stand still in a controlled environment. In that environment, the skeleton should have a way to hit the creeper, while trying to hit you, and the skeleton must not be within the creeper's trigger radius. (Note: If you hit the creeper before the skeleton shoots it, it will cause it to only target you until you are further than 16 blocks away or until it can no longer pathfind to you.)