1. Combine vinegar, beer, water, and Worcestershire sauce in small saucepan.
2. Add brown sugar, salt, garlic powder, cayenne pepper, black pepper, and onion powder to saucepan.
3. Heat over low heat.
4. Using brush or mop, slather mutton with marinade.
5. After mutton has finished cooking, bring marinade to boil and use it for a sauce to pour over mutton.