Put brisket in large stockpot, add season packet that comes with brisket. Pour whiskey/bourbon and beer over meat, add water to cover if needed. Bring to boil, skim off foam, and simmer 4-5 hours. Preheat oven 350 degrees. Remove brisket and place in baking dish. Add all vegetables to liquid, add more water if needed. Simmer 45 minutes. Mix syrup and mustard together. Spread over brisket and place in oven for 45 minutes to glaze.