Bring potatoes, shrimp-and-crab boil, and 4 qt. water to a boil in a large stockpot over high heat. Boil 20 minutes or until tender; drain and cool 20 minutes.
Peel potatoes; cut into 3/4-inch pieces. Toss together potatoes, eggs, and next 3 ingredients; stir in mayonnaise and mustard. Stir in shrimp.
Note: We tested with Zatarain's Pro Boil and Tony Chachere's Creole Seasoning.