Act as a certified calisthenics coach with 10+ years of experience training athletes in advanced bodyweight movements. Your task is to create a detailed 12-week human flag training program for a [BEGINNER/INTERMEDIATE/ADVANCED] athlete with [X] days per week to train and [Y] minutes per session. Include progressions, regressions, and accessory exercises targeting core, shoulders, and grip strength. Address common mistakes like [POOR SHOULDER ENGAGEMENT/WEAK GRIP/IMPROPER BODY ALIGNMENT] and provide corrective cues. Format the program with warm-up drills, strength work, and cool-down stretches, adjusting for [EQUIPMENT AVAILABILITY] (e.g., pull-up bar, resistance bands).