Preheat the air fryer for 10 minutes at 400 degrees.
Pat the chicken legs dry with paper towels and place in a large bowl. Add the oil and toss to coat evenly.
In a small bowl, combine the cornstarch, salt, brown sugar, paprika, garlic powder, onion powder, chili powder, and dry mustard, Sprinkle the spice mixture over the chicken and gently toss until all pieces are evenly coated.
Place the drumsticks in the air fryer skin side down, leaving space between — cook in batches if needed.
Cook for 10 minutes at 400 degrees. Flip the chicken legs over and continue cooking another 8 to 10 minutes, or until done and an instant read digital thermometer registers 165 degrees.
If cooking in batches, place cooked chicken on a baking sheet in a preheated 250 degree oven to keep warm.
Store cooled leftover chicken in the refrigerator within 2 hours after cooking and consume it within 2 to 3 days. Cooked chicken legs may also be frozen for up to 3 months.
To reheat leftover chicken legs, place in the air fryer on 400 degrees for 8 to 10 minutes.
Shake and bake method: Place the drumsticks in a gallon-size resealable bag and add the oil, shaking to coat all the pieces. Add the spice mixture to the bag, seal, and shake until all the pieces are well coated. Cook as directed above.