SQL Server trigger (update or insert with inner join problem)
How about changing the trigger to a BEFORE UPDATE? That way you can check the values before any action has taken place.

EDIT

OK so I think I understand what you are trying to do. How about this:

ALTER TRIGGER [dbo].[killertrigg]
   ON  [dbo].[tbl_pvporderview]
   AFTER UPDATE
AS 
BEGIN
  SET NOCOUNT ON;
  Merge killer as k
  Using (select serial, [kill] from inserted) as I (serial, [kill])
  On (k.serial = I.serial)
  When matched then
   Update set [kill] = I.[kill]
   When not matched then
   Insert (serial, [kill]) values (I.serial, I.[kill]);
END