Combine oyster sauce, sugar, water, and Kecap manis in a bowl.
Heat the oil and butter in a wok over medium high heat. Add the garlic, chiles, and ginger and cook until fragrant. Add the black pepper, white pepper, coriander, and green onion and stir fry for 30 seconds.
Add the oyster sauce mixture to the wok and stir well. Bring to a boil, reduce heat to medium, and simmer for an additional 5 minutes.