Add the frozen mango chunks, aged rum, simple syrup, lime juice, and ice cubes into your blender.
Secure the lid and blend on high speed until the mixture is smooth and frothy, about 30-40 seconds. You should see bright, icy swirls forming as the ingredients combine.
Stop the blender and check the texture — it should be thick, creamy, and icy. If it's too thin, add a few more ice cubes and blend briefly again.
Pour the slushie into glasses, allowing the vibrant orange and frosty appearance to shimmer as it flows.
Garnish with a lime wedge or a small slice of mango for a colorful finishing touch.
Serve immediately with a straw and enjoy the tropical chill with a spicy rum kick.