ML is pure evil/villain at first but when he falls for fl he slowly starts to change (C-Drama)

Maybe these?

• The Romance of Tiger and Rose (villain ML who changes when he falls for FL)
• Rewriting Destiny (not quite a villain, but ML is very cold and cruel until he falls in love with FL)
  
• Night of Love With You (villain ML)
• My Villain Husband  (villain ML)
• The Queen of Attack (kind of evil ML who slowly changes after he falls in love)
• Affairs of a Drama Queen (villain ML who changes after he meets the FL)
• Love Better Than Immortality (kind of villain ML who falls for FL)
• I Want to Live to the Finale (villain ML who changes when he falls for FL)
• Mr. Bad (ML is the villain in the story)
• Twisted Fate of Love (ML is an anti-hero with something of a cruel edge who changes a lot after he falls for the FL even to the point he gives up the rest of his revenge plot for her.
• My Lethal Man (not evil but definitely a dangerous sort of person who changes toward the FL as he falls in love)

and as a bonus

• Is Xian Zun Whitewashed Today? (BL, ML is evil/villain who starts to change because of the other ML)

+ 1 - Love Between Fairy and Devil

+1 Night of Love With You  - short series. FL who usually is a negative character in stories transmigrates into one as a heroine and the villain of the story falls for her. It's a rom-com.

Meteor Garden - ML is a bully.

Maid's Revenge - ML is a bit of a black sheep and FL believes he murdered her family.

Mission in Parallel  - FL transmigrates into the body of an abused wife and teaches her husband a lesson.

ML is an enemy of the FL's people:

• +1 Love Between Fairy and Devil
• +1 Till the End of the Moon
• My Uncanny Destiny

ML lies to, manipulates, or tricks the FL, treats her callously, or holds her against her will at first:

• Back From the Brink
  
• The Romance of Hua Rong
• Princess Agents

ML is a villainous or morally grey emperor:

• The King's Woman
• Story of Yanxi Palace
• Empress Ki - Korean drama but mostly set in China.

ML was designed / created to play a villainous role:

• +1 The Romance of Tiger and Rose
• Ru Hua Ru Tu

I wouldn't really call any of these MLs "pure evil". 

Different Princess - ML is the villain of the story and the FL is the author of her novel, she will enter it as the wife of the de ML but he will try to kill her on her first day in 

1 The Confidence

2  Unexpected falling. 

Both drama have same leads, many same actors, same director. The unexpected falling is unofficial sequel to the confidence, at least that was my feeling after watching them both, watch the Confidence first. ML is evil, toxic, posessive, jealous type but so damn hot... both leads are beautiful and hot chemistry, don't miss these dramas. More romance in second drama. Happy ending in second drama.