Once again, I went with Stark on this one
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After you complete missions 1 - 20 you will have all kinds of Soul Attack missions unlocked, including Beat Attack (Intermediate). This Beat Attack has nothing but those annoying hollow heads flying around in an area above the city streets. Usually, these guys are a pain to deal with unless you use your range attack, however Stark uses nothing but range attacks!
By the end of the 3 minutes I had 400 enemies down. Please comment if you have any questions.