Combine water, butter, sugar, and salt in a medium saucepan over medium-high heat. Bring to a rolling boil, stirring occasionally until the butter melts completely.

Remove from heat and immediately add the flour all at once. Stir vigorously with a wooden spoon until a smooth ball forms and pulls away from the sides of the pan, about 1 minute.

Transfer the dough to a large bowl and let cool for 5 minutes. Beat in the eggs one at a time using a hand mixer or wooden spoon, mixing until each egg is fully incorporated before adding the next. Stir in vanilla extract until the dough is smooth and glossy.

Prepare the mango sugar by grinding freeze-dried mango into a fine powder using a spice grinder or food processor. Mix with 1 cup sugar and citric acid in a shallow dish.

Heat oil in a large heavy-bottomed pot or deep fryer to 375°F. Fit a piping bag with a large star tip and fill with the churro dough.

Pipe 5-6 inch lengths of dough directly into the hot oil, using scissors to snip the ends. Fry 3-4 churros at a time without crowding, cooking for 2-3 minutes per side until deep golden brown.

Remove churros with a slotted spoon and drain briefly on paper towels for 10 seconds. Immediately roll the hot churros in the mango sugar mixture, coating all sides generously.

Transfer coated churros to a serving platter and repeat with remaining dough. Serve warm within 2 hours for the best texture and crunch.