Practice.
HTH

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Given I'm married w/2 kids and like the odd game of poker as well, the number of hours I've spent playing GH ever since the first one came out is really quite scary. And I still can't finish Free Bird (GH2, one of the best songs in the series, IMHO) on Hard, let alone Expert.
Lefty flip is a bugger though, agreed. Not much advice I can give. You just have to try and fire the attacks across at him at useful times, like when he's trying to collect an attack, although that does mean watching his notes as well as yours, which isn't easy, and hope you don't get hit with too many yourself. Practice some songs at Medium as well - when you go back to Easy it'll seem, well, easy. Been a while since I played GH3, TBH, GH5 and Band Hero recently.
Beating him is good though - you get a go on Through the Fire And Flames as you rise out of hell with no possibility of being Boo'd off. And it's like 8 minutes long

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