Begin by making the simple syrup. Bring sugar and water to a boil. One boiling, remove from heat and let cool. Once cooled, add mango and simple syrup to a food processor or blender. Blend until completely smooth. Set aside.
To make the salty chili sugar, combine coarse salt, sugar, and chili powder in a small bowl or plate and stir. Use a lime wedge to moisten the edge of the glass, then rim in the salty sugar. Fill glass with ice.
Add tequila, Grand Marnier, lime juice, and mango simple syrup to a cocktail shaker with ice. Shake for 15 seconds, then add to glass. Stir in jalapeño slices, mango, and a slice of lime. Drink up!