Step event

if (created==0)
{
    global.playerTime=self.time+1;
    future=instance_create(x,y,obj_boulder);
    future.time=self.time+1;
    created=1;
}

if (time==global.playerTime)
{
    visible=true;
}

if (time!=global.playerTime)
{
    // visible=false;
}

if (created==1)
{
    future.x=x+lengthdir_x(4,dir);
    future.y=y+lengthdir_y(4,dir);
    future.dir=dir;
}

Collision with wall

future.dir=180;