In a medium bowl, whisk together soy sauce, agave, garlic, sliced green onion, and black pepper. Add shrimp and mango. Marinade in the refrigerator for 15 to 30 minutes.
Place skewers in a shallow baking dish filled with cold water. Soak for 15 minutes. Pat dry with a paper towel.
Remove shrimp from marinade and add to skewers, approximately 4 to 5 shrimp per skewer.
Heat grill or grill pan over high heat. Season the grill with the oil. Once hot, grill shrimp skewers for approximately 2 to 3 minutes on either side. Remove from grill or grill pan once pink and opaque. Add to serving platter and sprinkle with chopped cilantro.
Stir together ingredients for the dipping sauce in a small bowl. Serve with shrimp skewers and lime wedges.