When using the soul-catching staff, enemies don’t spawn. Does this have something to do with the difficulty setting? Or is it something in the settings?
Try to increase creature spawn count in setings, there a lot of mobs spawns underground in caves tha you don’t see. Also you can click spawner to activate it, this can help.
There isn’t much better than a wide open game world in which you have essentially no limits and can alter the very landscape in which you play – that is, unless you add dragons, of course…