With Ping Pong students learn to deal with multiple player inputs as well as create a simple scoring system.
Ping Pong Instructions
///Bounce against walls -- Only Above and Below
//Back up ball before collision
x=xprevious;
y=yprevious;
//Bounce for vertical collision
if(place_meeting(x,y + vspeed, other))
{
vspeed = -vspeed;
}