When Ross hits the witch with the throne, a cloth is clearly used, not a person.
Though the game that the Midnight Society members play in the opening is a Game Boy, David explains that the button Eric presses resets it. The Game Boy does not have a reset button.
Though the Midnight Society members are playing with a Game Boy, it shows the back of the unit several times, it is clear there is no game cartridge in the device. The Game Boy was a cartridge driven hand held console, so there's no way they could have been playing anything.
The sound effects coming from the Game Boy prior to the tale are not actual Game Boy sound effects, but rather the generic beeps and boops used throughout the series for electronic games.
After the throne hits the witch, a stagehand can be seen scooting it along.