Via the MySQL Manual:

• Control Flow Functions (verified as done)
• String Functions string function support  #310
• Numeric Functions (appear done, not competely verified)
• Date and Time Functions support time function #236
• Bit Functions (appears done)
• Cast Functions (appears done)
• Encryption and Compression Support Encryption and Compression Functions #2632
• Information Functions Add remaining Information Functions #8438
• JSON Support remaining JSON functions from MySQL 5.7 #7546
• Aggregate Functions Call For Participation: finish the unsupported aggregate functions #7623
• Misc Functions Add remaining miscellaneous functions #8439