Prince Yu (Xiao Jinghuan)--Generally a manipulative political schemer. At one point blows up a fireworks factory just to frame his brother the Crown Prince, killing about a hundred innocent bystanders. Also tries to trick his other brother (Jingyan, the one actually good prince) into committing treason and getting caught and probably executed. Upon realizing Jingyan has a definite political advantage and that he himself will probably never be Crown Prince, he attacks the Emperor and Jingyan with a quite large army, the intent being to kill them both and claim Jingyan killed the Emperor, and take the throne for himself. Just in general he does a lot of bad things.

Prince Yu does have a sympathetic side; he badly wants his father's approval, and he has a tragic backstory which is pretty sad. But he wasn't actually aware of that tragic backstory until long after going down the path of villainy (like... it's to do with his birth mother and he has no idea about it until right before he pulls his whole "I'm going to murder my dad" scheme), and it doesn't change the fact that he gets a huge number of people killed. Other characters in the story find him everything from evil to vaguely distasteful. The main character, Mei Changsu, habitually calls him a "snake". Shen Zhui at one point says he wants a lightning bolt to fall on Prince Yu's head, and Jingyan seems to more or less agree with this viewpoint. Anyways. He's a villain.