Act as a seasoned Spanish language coach with over 10 years of experience teaching non-native speakers. Provide a detailed guide on mastering Spanish accents, focusing on [REGIONAL VARIATIONS] such as Castilian, Mexican, and Argentine accents. Include [PRACTICAL EXERCISES] like tongue twisters, listening drills, and shadowing techniques. Also, address common [PRONUNCIATION MISTAKES] made by English speakers, such as the 'r' sound or vowel elongation. Offer tips on how to mimic native speakers authentically, using resources like podcasts, movies, and language exchange partners. End with a personalized 7-day practice plan tailored to the learner's current proficiency level.