Both of these changes were reverted for Kirby Super Star Ultra the earlier line became "come meet your doom!" Inversely, a line where Meta Knight coldly insults his crew for dying on a sinking ship in their single-minded pursuit of Kirby was replaced with one where he agrees to their plan and thanks them for their loyalty. A fairly innocuous "Let us duel!" was replaced with " Prepare to Die!", pointedly avoiding one of Nintendo's stricter rules at the time.
The Revenge of Meta Knight mode received some minor changes seemingly to make it more "hardcore"-the most notable of which is the name itself (from "Meta Knight's Counterattack").
The game was an installment of the ineffably cute Puyo Puyo series rebranded for an American audience, giving Kirby a personality more similar to Puyo's protagonist, Arle. Kirby's Avalanche shows Kirby as a Jerkass who acts sarcastic and mean to his friends, saying things like "Oh, I'm so scared" and the like."He used to be such a good boy." The commercial for those games also established Kirby as a criminal. Also compare the commercials for Kirby's Dream Land and Kirby's Adventure, to say nothing of the magazine ad for ◊ Kirby's Avalanche and Kirby's Dream Course. A Kirby's Dream Land 2 commercial aired in the US turned Kirby, Rick, Kine, and Coo into scowling tough guys (or, you know, as tough as an 8-inch high puffball and his similarly-sized friends can be) roughhousing some Hell's Angels, ending with a menacing voiceover by Tony Jay. Earlier in the series, this applied to advertisements rather than box art.It seems that Europeans are expected to be able to stand happy Kirby.
American culture, while not having any outright animosity towards it, tends to associate the bright, colorful, and innocent with childhood and immaturity, and generally have more of a preference towards works that are manly and edgy. Japanese culture, in general, is very accepting of cuteness anyplace, and will take it in stride. This has to do with Values Dissonance and Americans Hate Tingle to a lesser extent. Sometimes this trope goes the other way, too: an American character may be made cuter for the Japanese release. This is often done to characters who were originally intended to be cute. Maybe it's as simple as adding Angry Eyebrows, or maybe the character's model is completely redone. When a Japanese game is released Stateside, there's a tendency to make the box art, or even the character models, a little more hardcore.