diabolical

A diabolical person or plan is very bad and sometimes even evil. This means they might think about causing harm or getting an unfair advantage.

The word "diabolical" is often used to describe something that's not just bad, but really cleverly planned or carried out in a sneaky way. Think of a villain from a movie or TV show who comes up with a wicked scheme to get what they want. That plan might be diabolical because it's so well thought out and manipulative. People also use the word to describe something that seems clever, but is actually just mean-spirited or unfair, like cheating in a game or a company exploiting workers for profit.