Controller allows quick-edit and animation or action trigger .
The Controller can be found on Settings page when editing an Overlay project (as mentioned in Editing Overlay documentation)
Content of the Controller can be different because it detects what type of overlay is used and what elements need to be triggered or edited.
As an example, the Controller can have one single button (Spin Wheel or Flip the Coin) — or multiple elements like in the below image
On left side (above image) is a simple Lucky Number mini-game overlay and on the right side is the Controller
Can be used from mobile devices too.