Cook tomatillos, tomatoes, serrano peppers, chile de arbol peppers, and 3 whole garlic cloves in a saucepan over medium-low heat until mixture is juicy and peppers are tender, about 10 minutes. Remove and discard garlic cloves.

Pour mixture into a blender and blend until smooth, about 1 minute. Mince 1 garlic clove and mix into sauce. Season with salt and set aside.

Mince remaining garlic clove and place into a skillet. Add pork, cover the skillet, and cook over medium heat, stirring occasionally, until pork is no longer pink and the juices run clear, about 30 minutes.