In a large bowl, mix the cabbage, carrot, sweet onion, green onions, and dill pickle.
In a separate bowl, whisk together the mayonnaise, buttermilk, dill pickle juice, vinegar, mustard, sugar, cayenne pepper, and 3/4 teaspoon salt. Mash together the remaining salt and garlic, and whisk into the dressing. Drizzle dressing over the slaw, and toss to coat. Cover and refrigerate 8 hours, or overnight, before serving.