The recent stock market tumble has cast a shadow over the outlook of big corporate takeover deals in South Korea as buyers and sellers are taking stock of its pluses and minuses, market watchers said Wednesday. Bearing the brunt of the recent financial turmoil sparked by the first-ever U.S. debt downgrade and the European fiscal crisis, the main Korea Composite Stock Price Index (KOSPI) tumbled as much as 18 percent this month.