— Steve to Hal and Jeff
Steve is a happy-go-lucky Piranha Plant in the Bowser's Kingdom show who Hal and Jeff find extemely annoying. He doesn't mean to be annoying but somehow manages to be that way. A common theme is for Hal and Jeff to take out their frustration on Steve because he is always happy and incredibly naive. He is voiced by Steven Button.
In Episode 1, Steve overhears Hal and Jeff talking and pops out of a pipe to say hello. He greets the pair with his typical expression of "HI GUYS!", but Hal tells him that he doesn't want Steve to be involved in their conversation and rudely shouts "Fuck you, Steve! Fuck you!" Despite being spoken to in such a manner, he is still keen to help them out and spits a fireball at a nearby Shy Guy on Jeff's orders. Hal thanks Steve but then tells him to get lost, forcing Steve to go back down his pipe with a farewell cry of "BYE GUYS!"
In Episode 2, Steve tries to join a group of Shy Guys who are planning to take over the world. He fools them all by wearing a Shy Guy mask, and even though he accidentally tells them his name is Steve before quickly changing it to "Shy Guy", the group still welcome him with open arms.
In Episode 4, Hal and Jeff are sent to Club Iggy, a nightclub either owned or named after Iggy Koopa, to replace the old bouncer. This is soon revealed to be Steve, who greets the pair and asks if they are going to work alongside him. Hal tells him that they are in fact replacing him and that he's terrible at his job, but Steve is puzzled by this. Hal and Jeff then see exactly why Steve got fired when Mario walks by; instead of stopping him from entering the club or even attacking him, Steve shouts "Hi Mario!" and lets him walk straight in. Steve tells them that Mario is a regular there and that he has a strong passion for dancing, leading Hal to tell Steve that the world would be a better place if he just put a bag over his head and never took it off. Later, when Hal and Jeff are parking Bowser's clown copter, they see Steve on a remote platform with a paper bag over his head. Once again, he happily greets them both and asks what he's meant to do now, to which Jeff responds "Die". After asking whether he's dead yet, Hal informs Steve that he needs a plastic bag in order to kill himself and that he's undeniably stupid for not knowing it. As he and Jeff fly away, Steve says to himself that he still thinks "those guys are swell". When Hal and Jeff eventually return, they see Steve dead with a plastic bag over his head. Having already killed two people during the episode, Jeff claims Steve the third victim. Hal disagrees, stating it was a suicide and not a murder, but Jeff argues that they told him to do it and are therefore responsible. Hal responds by saying they aren't responsible for Steve's own stupidity.
At the end of Episode 5, three tribal Shy Guys who Jeff had hired as Witch Doctors to bring back the dead stand next to Steve's body and perform a special dance. Steve is momentarily revived.
In Episode 7, Steve and his cousin Petey Piranha form Team Piranha Plant during the Villains' Olympics. They come third place on the leadership board and earn a lifetime's supply of milk as a reward. Unfortunately, Steve indicates that Petey is lactose intolerant (as Petey is heard vomiting in the background).
In Episode 8, Hal and Jeff find themselves lost in outer space after falling off Bowser Jr.'s airship. They land on a small planet with a single green pipe on it, from which Steve appears. Once more he gives them both his typical greeting and asks what they're doing all the way out in space. The pair are then introduced to Steve's partner, a giant blue dinosaur creature, that he had a baby with. When Hal sees an enormous egg on the planet's underside, he asks Steve how he could have possibly created something like that, to which Steve responds he was both "drunk" and "in love". The egg soon hatches to reveal a Dino Piranha, which takes after its father with the typical "HI GUYS!" expression. Steve then watches as his child begins relentlessly chasing Hal and Jeff around the planet.
In Episode 10, Hal mentions during a behind-the-scenes interview how he would like to sell out with moneymaking merchandise, such as a t-shirt with an 8-bit Steve logo saying "HI GUYS!" Hearing this, Steve appears and tells the interviewer that "Hi guys!" isn't his catchphrase. According to Steve, his catchphrase is "Who ate all the ketchup?", but the interviewer reminds him that he's never said that in his life. Steve gets annoyed and disappears into his pipe.
Steve appears yet again in the Bowser's Kingdom Movie, where he is shown in a field happily talking to a small group of flowers. Hal and Jeff come strolling along and immediately know Steve is nearby when they hear an "irritatingly cheerful voice". Steve greets them and says how wonderful today is, but Hal is clearly not in the mood for high spirits and tramples the group of flowers in his anger. For the first time, Steve becomes sullen and glum and disappears into his pipe. Jeff tells Hal that what he just did was a little harsh, but Hal says it's just Steve and that he isn't worth worrying about. They then proceed to dress up as Mario and Luigi on Bowser's orders and sneak into Peach's Castle before kidnapping her. However, they are both unaware that Steve is plotting revenge against them, having finally had enough of their arrogant attitude towards him. He spreads a false rumour that Hal and Jeff are going to bag the princess for themselves, and when this news reaches Bowser's ears, he sends his minions to find and destroy them. Near the end of the movie, Hal and Jeff are confronted by a great number of enemies, but the Karate Duo Number 1 are able to deal with them all and give them both time to escape with Princess Peach. As the trio hide in an underground chamber, they hear a faint and ghostly call of "Hiii guuuyyys" which creeps them out. Steve unexpectedly appears from a pipe and Hal and Jeff are surprised to see him. After telling him that they aren't in the mood for his waffle and that they've already had enough trouble as it is, Steve reveals to them that he was the one who caused it. Mario and Luigi then drop down behind Hal and Jeff and while they're distracted, Steve snatches Peach from them with his long vines and disppears into the pipe with an evil laugh of triumph. Mario and Luigi beat up Hal and Jeff before travelling to Bowser's Castle, where Steve is presenting Peach to Bowser. The brothers land on Steve, squashing him, before knocking out Bowser and rescuing Peach.
During Episode 666, Steve is one of the many creatures of the land that has turned into a zombie. Whilst Hal and Jeff are fighting off an undead hoard within a castle on the Doughnut Plains, the zombified Steve bursts out of the ground and, with a monstrous cry of "HI GUYS!", swallows Geno and disappears. However, in one of the two separate endings, Geno uses a laser beam to destroy Steve from the inside and saves Hal and Jeff by obliterating the other zombies.