What can I almost make from dark rum, mango syrup, Malibu coconut, and gin?

Based on the ingredients you have—dark rum, mango syrup, Malibu coconut, and gin—there isn't an exact match among the cocktails provided, but we can get creative to come up with something close. You primarily have ingredients that are reminiscent of tropical cocktails.

Consider making something similar to the Mango Mixer or the Tropical Sunset. While these cocktails don’t use all of your specific ingredients, you can adapt their recipes for a delightful concoction.

1. Mango Mixer Inspiration: Mix the dark rum with mango syrup to capture the essence of mango juice. Add a hint of lime juice if you have it, to balance the sweetness with some tartness. A touch of pomegranate or a similar fruit juice can add some complexity, and adjust the gin amount so it doesn't overpower the tropical flavors.
2. Tropical Sunset Inspiration: Create a version by combining the Malibu coconut with dark rum for a richer base. Include the mango syrup to mimic the tropical fruit tones. A splash of orange juice (if available) can enhance the citrus element, bringing it closer to the Tropical Sunset vibes.

To serve, shake your ingredients with ice and pour into a highball or cocktail glass. For aesthetics, you can drizzle a bit of grenadine if you have it to create that lovely layered look often found in tropical drinks. This way, you leverage your current ingredients while approaching the delightful, fruity, and refreshing experience highlighted in the Mango Mixer and Tropical Sunset cocktails.