Blend the base:
Add watermelon, mango, ice, milk, yogurt, sweetener, and lime juice to a blender.
Blend until smooth:
Blend on high until it's icy, creamy, and smooth. You can add more milk for a thinner texture or more ice for a slushier one.
Swirl and pour (optional):
Drizzle mango purée inside your cup if you want that splashy look.
Top and enjoy:
Pour into a tall glass, top with whipped cream and fruit bits if desired, and serve immediately with a straw.