1. Do not assign the pointers in the while loop, just put it in begin of the action:

Code:

---

entity* p1;
entity* p2;

action play1
{
   p1 = my;
   while(p2==null){wait(1);}
   while(1)
   {
      my.x += 2 * key_force.x * time;
      if (my.x > p2.x)
      {
         my.z += 5 * time;
      }
   wait(1);
   }
}

action play2
{
   p2 = my;
   while(1)
   {
      my.x += 2 * joy_force.x * time;
      wait(1); 
    }
} 

---

This should work. Dont forget you need to move p1 to a point where its x is superior do p2, otherwise it wont work.