Rim a chilled glass with Tajín.
In a shaker filled with ice, add the tequila, lime juice, blood orange juice, and cranberry syrup.
Shake until chilled, about 10–15 seconds.
Strain into your prepared glass filled with fresh ice.
Top with grapefruit soda and gently stir.
Garnish with two chili peppers on the rim to create your “devil horns.”