My courses (stupid internet connection...)
ODFY-0000-0156-B31B - Pirahna Spin Jump
2B35-0000-0156-9D75 - P is for Puzzle
426F-0000-0150-97D9 - Pipeship Kaizo
CDCB-0000-0150-974B - Ghost House Maze
EBB8-0000-0150-96E5 - Mario Kart 8-bit
3FAA-0000-0150-960B - Bob-omb Airship
A9B5-0000-0117-358D - Platform Panic Grinder Attack
9BF3-0000-0104-5579 - Coinship
DB11-0000-0101-E988 - Ridiculous Wall Jumps
37B5-0000-0101-E951 - Up and Down
Of these, I like Bob-omb Airship the best. The hardest, you say? That's up to you, but they're all relatively hard.
ODFY-0000-0156-B31B - Pirahna Spin Jump
2B35-0000-0156-9D75 - P is for Puzzle
426F-0000-0150-97D9 - Pipeship Kaizo
CDCB-0000-0150-974B - Ghost House Maze
EBB8-0000-0150-96E5 - Mario Kart 8-bit
3FAA-0000-0150-960B - Bob-omb Airship
A9B5-0000-0117-358D - Platform Panic Grinder Attack
9BF3-0000-0104-5579 - Coinship
DB11-0000-0101-E988 - Ridiculous Wall Jumps
37B5-0000-0101-E951 - Up and Down
Of these, I like Bob-omb Airship the best. The hardest, you say? That's up to you, but they're all relatively hard.