Singer Seo In Guk is back with a new single and he wants to "Shake It Up" with you on today's episode of Mnet's�'M! Countdown'. "Shake It Up" is the work of American composer Drew Ryan Scott, who's already worked with countless other Korean singers.�Producer Hwang Se Jin, who's known for his stunning arrangements of Jang Hye Jin's songs on MBC's 'I Am a Singer', also contributed as the project's head director. With such a strong foundation of support, Seo In Guk's "Shake It Up" will surely be the summer theme song for many years to come. Check out his fun comeback stage below!