I can barely understand what you say, would you have time to do it, Fergus?

Here it is with comments to indicate the main changes I made. I have not tested this. It will be up to you to do that.

sub stalemated kingpos:
  store;
  local from piece to movetype ltm;

  // store the value of last_type_moved into another variable
  set ltm last_type_moved;

  set movetype MOVE;

  if isupper space #kingpos:
    def friends onlyupper;
    def friend isupper #0;
  set cspaces var wcastle;
  else:
    def friends onlylower;
    def friend islower #0;
  set cspaces var bcastle;
  endif;

  // While the royal piece is called the King in these comments,
  // it may be any piece. These variables determine what the royal piece is.
  set royal space var kingpos;

  store;

  // Can any piece legally move?
  for (from piece) fn friends:
    for to fn join const alias #piece "-Range" #from:
      if fn const alias #piece #from #to and not fn friend space #to and onboard #to:
        move #from #to;
        if not sub checked cond == #from #kingpos #to #kingpos:
          setlegal #from #to;
          // Whenever a piece is moved for the sake of trying out a potential move, the value
          // of last_type_moved should be changed to match the type of the piece moved.
          if isupper #piece:
            if != const alias #piece White_Joker:
              if != const alias #piece White_Pawn:
                set last_type_moved const alias #piece;
              else:
                set last_type_moved Black_Barren_Pawn;
              endif;
            endif;
          elseif != const alias #piece Black_Joker:
            if != const alias #piece Black_Pawn:
              set last_type_moved const alias #piece;
            else:
              set last_type_moved White_Barren_Pawn;
            endif;
          endif;
        endif;
      endif;
      restore;
      // Each time the evaluation of a potential move is over, and the position has been
      // restored, the value of last_type_moved should be restored to its original value.
      set last_type_moved #ltm;
    next;
  next;

  // Castling code removed, since Apothecary Chess does not include castling.

  // All done. Set $legalmoves and return;
  return cond count system legalmoves false true;
endsub;