- “With his fiery breath, Baby Bowser can defeat enemies and melt ice. Breathe fire by pressing Y button. Keep in mind that Yoshi can't make eggs with Baby Bowser on his back, but he can still pick them up and throw them.”
- —Description, Yoshi's Island DS
Super Mario World 2: Yoshi's Island
In his debut, Super Mario World 2: Yoshi's Island, Yoshi must enter the castle and work his way to Bowser's bedroom, which is filled with toys. When Kamek tells Yoshi to hand over Baby Mario, Baby Bowser wakes up and tells them to be quiet cause he is "sleepy". Kamek is instantly filled with fear. Baby Bowser stomps on Kamek before noticing Yoshi. Thinking Yoshi is a donkey, he tries to ride him several times but Yoshi knocks him out. Kamek returns and "helps" Baby Bowser by turning him into a giant, destroying most of the castle in the process. As a giant he appears more like his grown up self. After a long, epic battle Bowser is reverted to his baby self and is unconscious. Kamek is horrified and calls Yoshi a meanie before flying off into the night with Baby Bowser. Yoshi then frees Stork and Baby Luigi and the stork flies away with the babies into the night.
The giant version of him is the biggest boss in the game. Even though he is the final boss he is not the main antagonist, as Kamek is. He is also one of the two only characters who talk in the game.
In Yoshi's Story, Baby Bowser becomes jealous of the Yoshi's happiness, so he steals the Super Happy Tree and casts a spell to turn the entire island into a story book. The Yoshi's then set out to revive the Super Happy Tree. The last page of the story book is Bowser's Castle. After fighting Baby Bowser they get the Super Happy Tree and restore happiness to the island.
Yoshi's Island DS
In Yoshi's Island DS, Baby Bowser helps Baby Mario, Baby Peach, Baby Donkey Kong and Baby Wario to save Baby Luigi. While riding on Yoshi he can breathe fire, which can defeat enemies and light up torches, as well as performing a lot of the moves that an egg can do (destroying ? clouds etc.) but it stops Yoshi from being able to lay eggs (he can still pick them up and throw them.) At the end of world 4, he gets taken by Kamek, but rejoins the babies later on (in Bowser's Castle) However he betrays the other babies when they reach the end of his castle. The other babies and the Yoshi's succeed in defeating Bowser and rescue Luigi. When he betrays Yoshi near the end of the game, his attack moves include breathing fire at Yoshi, jumping, breathing fire downwards, then ground-pounding, after having six eggs thrown at him, he will be defeated and Yoshi will then have to fight Bowser.
Baby Bowser makes a cameo in Yoshi Touch & Go as one of the selectable high score icons. He also appears when Yoshi gets a Game Over with over 3000 yards on the Challenge Mode, laughing with Kamek.
Yoshi's New Island
Baby Bowser returns in this game after not being seen for 7 years, wanting to turn Egg Island into a resort. At the end of the game, a similar scene of him awakening from slumber and fighting Yoshi begins, with him turning giant after. After he is beaten, his future self reappears wanting to protect him making Yoshi defeat him.
Yoshi's Woolly World
In this game, Baby Bowser wants to have enough yarn to make himself a castle. In this battle, Yoshi must attack Baby Bowser by throwing a yarn ball at him and then ground-pounding him. After the first phase, Kamek makes him a giant using the Wonder Wool. In this phase, Yoshi must unravel giant yarn balls to get smaller yarn balls to throw at eight weak-points, shown as magenta Wonder Wools on Baby Bowser's body. After this, Baby Bowser is taken back by Kamek to the moon, before Kamek is scared by Poochy, causing him to drop the tyke.
Yoshi's Crafted World
Baby Bowser and Kamek are once more the main antagonists in Yoshi's Crafted World. In this game, he steals the Sundream Stone with Kamek, wanting to find the five Dream Gems from it. However, Baby Bowser joins Kamek in the quest, dismantling the train in the first level and making the bosses. He is also the final boss of the game, with his phases being inside a large robot and then growing to a large size once more.
Mario and Luigi: Partners in Time
Baby Bowser's first and only appearance in the Mario & Luigi series is in Mario & Luigi: Partners in Time, where he is a major antagonist. He first appears at the beginning of the game, in an attempt to kidnap Baby Peach. Luckily, Baby Mario and Baby Luigi show up in the nick of time to play with Baby Peach. After Baby Mario defeats him however, the Shroobs attack Princess Peach's Castle. Fortunately, everyone manages to escape on Baby Bowser's Koopa Cruiser. On the way to his castle, Baby Bowser picks the Mario and Luigi from the future to get Baby Peach to stop crying. On the Koopa Cruiser, he receives a transmission from Princess Shroob at Shroob Castle. She tells the crew something in the Shroobs' language and shoots down the Koopa Cruiser with a Shroob missile.
Baby Bowser is flung away from the Koopa Cruiser on the impact, into his castle. Eventually, he realizes that the Mario Bros. have stolen the Cobalt Star Shard from his castle and tracked the Bros. down at the Vim Factory, where he swipes both his Cobalt Star Shard and the one the Bros. have just snatched from Swiggler.
Baby Bowser then flees to the peak of Yoshi's Island with his caretaker, Kamek, where he orders Kamek to snatch the Yoshi Cookies from the Yoshis. When the Mario Bros. catch up to Baby Bowser at the peak, he scarfs down all the Yoshi Cookies, but starts choking. Baby Bowser then leaves to the other side of the peak after Kamek had given him some "evil" milk. After the Mario Bros. defeat Kamek, they corner him at the other side of the peak. Without thinking his plans through, Baby Bowser eats the Cobalt Star Shards. Soon after, he and the Mario Bros. are eaten by Yoob.
Inside Yoob, Baby Bowser, along with the Yoshis already eaten, are put inside a Yoshi Egg. When the Mario Bros. confront Sunnycide, a monster within Yoob, he throws the egg Baby Bowser is in at Luigi, breaking it open. After the Mario Bros. defeat Sunnycide, Baby Bowser and all of the swallowed Yoshis escape Yoob.
Back on Yoshi's Island, Baby Bowser informs the Yoshis that he saved them from Yoob. Having believed him, the Yoshis give him the rest of their Yoshi Cookies when the Mario Bros. and Toadbert show up and tell the Yoshis that he is lying. Baby Bowser then eats all of the Yoshi Cookies and gets sick. He vomits the Cobalt Star Shards, which, seemingly with a mind of their own, hit him and fling him off of Yoshi's Island.
Later on, Baby Bowser heads off to Thwomp Volcano to build a new castle, where he meets his future self, Bowser. After a minor argument, Baby Bowser and Bowser team up, not knowing the other ones identity, against the Mario Bros.. They end up being beaten after the battle and flung into the sky by a Thwomp, where Bowser ends up in a Time Hole and Baby Bowser ends up on top of the Shroob Mothership.
Baby Bowser shows up again after the Bros. have defeated Princess Shroob and despite objections, he put the Cobalt Star Shards together and completed the Cobalt Star, releasing Elder Princess Shroob. Baby Bowser is then turned into a Shroob Mushroom. Baby Luigi's tears later turn him back to his normal state. Baby Bowser shows up at the end of the game going home and complaining about losing the Cobalt Star.
Baby Bowser shares many physical qualities with his adult counterpart. They both have red hair and black cuffs on their arms. Baby Bowser has cuffs on his neck in Super Mario World 2: Yoshi's Island and in Yoshi's Story. In these appearances, as well as in Yoshi's Island DS, Baby Bowser appears with spiked cuffs, while in Mario & Luigi: Partners in Time, his cuffs appear with no spikes. Like Bowser, Baby Bowser has two red eyebrows, a green shell with spikes and two small nostrils on his nose. Baby Bowser also has claws on his hands and his feet. Unlike Bowser, Baby Bowser either has no horns or his horns are small and stubby, much like Bowser Jr.'s, depending on the game.
His personality is similar to Bowser Jr.'s. A spoiled child, Baby Bowser frequently throws tantrums in hopes that his minions, Kamek and the Koopa Troop will give him what he wants. He is greedy and very gluttonous, as shown in Mario & Luigi: Partners in Time, where he eats a huge pile of Yoshi Cookies and the Cobalt Star. Toadbert calls him a "Little Piggie". He even insulted his future self in Yoshi's Island DS.
- In Yoshi's Story, Baby Bowser is bigger than Yoshi. Though Yoshi was a baby in this game.
- Along with Baby Wario, he is the only baby from Yoshi's Island DS absent from Mario Super Sluggers.
- Baby Bowser, alongside Froggy is the only boss to be fought at one point without being enhanced by Kamek.
- His official artwork in Yoshi's Island DS has him on the back of a Yellow Yoshi, which is impossible, as where the Yellow Yoshi's are only found in forts, Baby Bowser is never found in there.
- Baby Bowser is the only baby who isn't voiced by his voice actor for his adult counterpart.
- The fight with Baby Bowser in Yoshi's Island after he transformed was known for frightening lots of young children given the boss fight's surprisingly serious and suspenseful tone, final bosses in Yoshi games have notably lightened up to prevent this from happening again.