I know this is of no importance at all, but you could get rid of one of these if statements as far as I know:
Code:

---

action arrowBox
{
   var counter=0; // counter has initial value of zero
   while(1) // continue firing indefinitly
   {
       if(counter == 50) //play with this number(amt of time b/t firing an arrow
       {
           you = ent_create(arrowMDL,my.x,arrowFly); //create new arrow
       }
       counter += 1;
       counter %= 50;
       wait(1);
   }
}

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