Whisk ketchup, chicken broth, egg, soy sauce, chile-garlic sauce, oyster sauce, tamarind paste, fish sauce, and palm sugar together in a bowl.
Stir shallots, garlic, oil, ginger, and serrano pepper together in a pot over medium-high heat. Saute until sizzling, about 2 minutes. Add crab to pot, cover the pot with a lid, and shake until crab is completely coated in shallot mixture. Remove lid and cook and stir until heated through, about 3 minutes.
Pour ketchup mixture into pot, reduce heat to medium, and cook and stir until sauce thickens and crab is hot about 5 minutes. Remove from heat; stir in cilantro and green onions.
