Greatestest Hits requires the new Spider Dance Boss from the Lost Chapter update, for a grand total of 8 bosses. Add any other two songs to the playlist to combine it with Greatest Hits.
Despite what the description says, you can unlock Hendrix Level (and also Chill) in the Playlist gamemode. Most people recommend Cascade or Dance of the Incognizant as the easiest dashless S ranks, but just choose the level you're best at!
If you have 3 or 4 controllers, it's actually more efficient to play hardcore challenges locally to grind beat points, since all of the players contribute towards your beat point count. This will save several hours, but it is quite boring. Not at all required for completion, and playing online is not too much slower, and also much more fun! The choice is up to you.
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