If desired, rim your glasses with tajin by running a lime wedge around the edge to moisten it, then dipping it in tajin to adhere.
In a high-speed blender, combine the mango, tequila, lime juice, Cointreau, agave, and salt. Blend until smooth.
Add 2 small handfuls of ice and blend. Blend, then taste and adjust the margarita as desired. If you'd like it thicker, continue adding ice until your desired consistency is reached.
Pour into glasses and enjoy immediately, garnished with additional lime.