Halloween Horror Movie Marathon Midnight, Saturday October 27-noon, Sunday, October 28 Coolidge Corner Theatre, Brookline, $20 Bostonist has never understood how The Monster Squad (1987) gained its cult following, but we know better than to argue with its partisans, who will likely be out in force Saturday night. The film kicks off The Coolidge Corner Theatre's 5th Annual 12 Hour Halloween Movie Marathon, which begins at midnight, Saturday and lasts until noon, Sunday. The Monster......