 Shares of Six Flags Entertainment Corp. SIX, 5.78 tumbled 8.8 in premarket trading Thursday, after the theme park operator reported second-quarter profit and revenue that fell well below expectations, as a big attendance miss offset higher spending per guest. Net income fell to 45.4 million, or 53 cents a share, from 70.5 million, or 81 cents a share, in the year-ago period. 