Somewhat inconsistent in Jack Spicer's case. He started off as a legit bad guy and an intelligent one at that. He built his own robots, and on several occasions, was shown as being able to match and defeat the Xiaolin Warriors in showdowns. Hell, Jack has taken over the Earth in two alternate timelines and did a damn effective job at ruling it, in one of the timelines he was even said to be a threat to the entire universe. By the final two episodes, he's portrayed as so stupid he has to write "This way up" on his underwear, however in episodes leading up to the finale, he still had burst of competency, as he was able to hold his own against Omi in combat and even took over Chase Young's fortress overnight. Throughout most of Xiaolin Chronicles however, Jack was a complete joke lacking a threatening bone in his body. See Villain Decay.
Chase Young is more obsessed with destruction and being evil for the sake of evil in Chronicles than he ever was in the original series, where he had more clear motives. He also laughs evilly far more often.
The protagonists had their fair share, too:
Omi began with his arrogance being mostly scarce and well-meaning, with it being implied that he wasn't so much egotistical, just eager to teach his friends everything he knew. Around the middle of Season 2, his ego started to get progressively bigger and bigger to the point where he would often insult Raimundo in the latter's presence and rub the previleges he received in the other monks' faces. Additionally, his sexism towards Kimiko was more of a sign of his cultural naivety in the first season and it should be noted that it never comes up again until his Flanderization, where he takes great pride in being a Straw Misogynist.
In the first season, Kimiko started out as a Genki Girl and a Deadpan Snarker who, while having the occasional Berserk Button, was mostly easy-going and acted as a Cool Big Sis to Omi and defended him from Raimundo's bullying. Come Season Two, her Hair-Trigger Temper is much more prominent, and she constantly beats up Omi for his sexist remarks towards her. Her snarky tendencies were taken up to eleven, turning her into a flat-out cynical, violent girl who gets angry at the drop of a hat.
Clay avoided this in the original show, but gets hit by this in Xiaolin Chronicles. In the former, he was known for being a soft, easy-going cowboy with a huge appetite and a realistic love for animals, which he cared for and was very knowledgeable about. In the latter, his interest in animals has become so exaggerated that it's literally outright shown that he's in a relationship with a goat named Molly and constantly waxes poetic about the butts of baboons that he "can't keep his eyes off of", baby goats' butts, the "soft, mushy lips" of his goat girlfriend "Molly", etc.
Dojo's close relationship with Master Fung started going in the direction of his being a servant of the latter until it grew almost to the point of Ho Yay. Later in Chronicles, Dojo seems to be outright and obsessively in love with Master Fung, to the point where he breaks down emotionally whenever the two are separated.
