We highly recommend having a Cardboard V2, which is any headset that has the capacitive touch button. The Cardboard V1’s magnet switch IS supported, but may not work consistently. Joysticks should work automatically with the game if you would rather use them instead of walking-in-place. By default, you will only move forwards and backwards with the joystick (to combat nausea), but there is an option in the settings menu (tilt to allow for full joystick movement.
Positional tracking enables highly immersive experiences on PC VR platforms (Vive/Oculus), such as walking input, but this isn’t available on mobile VR platforms, with as a result that many mobile VR apps are simple look-and-see or rollercoaster experiences. Gravity Pull was built using the VR-Step plugin (see Unity Asset store https://www.assetstore.unity3d.com/en/#!/content/60450) (patent pending). VR-step significantly increases existing interaction options of mobile VR platforms (Daydream, Gear VR, Cardboard) and lets you build highly immersive experiences that are usually only found on PC VR platforms.