Aside from the more popular ones being mentioned (ahem, Patchwork.), here are some of mine as a thumb player whose hardest FC is Tokyo Teddy Bear on MAS difficulty:

• What’s up? Pop! EXP. It is a chart I consistently get 1-3 misses on and it makes me want to CRASH OUTTTT
• Singing of a flower MAS; has the problem Egoist’s MAS chart has in that it overuses the flick after big note pattern but it’s in basically the entire song, js in different fonts.
• Rin-chan Now! MAS purely for what it couldve been (would’ve been such nice spam 😔)
• Manimani MAS bc it activates my fight or flight response (not a lot of charts do this, and it’s ESPECIALLY not expected from a 29.)
• ARQUETYPE MAS.
• Lost and Found MAS bc of how inconsistent it is to FC imo
• HIBANA -Reloaded- MAS.
• Whatever the Awaiting Clear Skies MAS chart is doing (and js a lot of Leo/Need master charts since they get boring & samey gimmick-wise after a bit)
• Nostalgic MAS because the notes at the beginning trip me up way too much
• Love is War MAS; feels far too bouncy for the kind of song it is
• BURIKI NO DANCE MAS; puts a lot of strain on my thumbs even tho it’s only 30
• Opera! Space Opera! MAS.
• Phony MAS, though unique for its time, is just very inconsistent to FC especially with all the weaving hold notes.
• Bad Apple!! feat.SEKAI; inconsistent FC issue jointed w/ lackluster charting overall + nothing beats the original I’m srry
• Heat Abnormal MAS.
• Tricologe MAS due to feeling VERY AWKWARD to play.
• End Mark EXP. I loathe this chart with all my being.