The Pi does require some sort of connection to be controlled and to run correctly. To make a standalone device, you would need to set up an access point with our plugin „Access Point Setup“. This way, the Pi creates its own WiFi network to access from your smartphone/tablet.
Here is an instructable I did on it: http://www.instructables.com/id/Raspberry-Pi-Mobile-Media-Center-with-Smartphone-C/
And here is the plugin page: https://www.max2play.com/en/portfolio/plugin-access-point-2/