Junker (called Super Ultra Great Mega Trashy Monster Junker Bot by Midbus) is a boss fought near the end of Mario & Luigi: Bowser's Inside Story. It is a robotic creature resembling a trash can. It is helped by several smaller monsters known as Junker Cans.
Junker is encountered while infiltrating Peach's Castle Garden near the end of the game. Upon entering a certain area of the garden, Starlow will comment that there is a lot of garbage laying about. After Mario and Luigi progress to the end of this area, Midbus appears, holding some sort of remote control. When it is activated, Junker springs to life from the piles of garbage laying around the area. After Midbus's attempts to control it fail, he smashes the remote and allows it to fight the Mario Bros. on its own. Midbus's attempt to control the Junker may demonstrate why it was in the garbage in the first place, as it began to dance when he commanded it to attack.
 Battle Strategy
In battle, Junker has a variety of attacks.
- One attack consists of throwing a bucket over either Mario's or Luigi's head. The brother will then stumble around blindly while Junker throws Thwomps at him. Players must cause the brother to jump with good timing to avoid the attack. If Mario or Luigi are hit by the Thwomp, they may get dizzy. This attack is a reference to the Super Famicom game Mario & Wario.
- Another attack involves throwing two balls of metal scrap at a bro, then attempting to ram him. The Mario brother in question must jump onto the balls, then jump over Junker as it attempts the ramming portion of the attack.
- A third attack consists of emptying the garbage from one of the Junker Cans that follow it. Often, this garbage will consist of random enemies that go after the Mario bros, which include: Cheep Cheep, who will jump over the Mario Bros., which will hurt them when they jump, Bob-omb, who will first light its fuse before charging, and Scutlet, which will immediatly charge after coming out. It will also have useless stuff like a pair of briefs and a wad of paper. Once several enemies have attacked, the Junker Can will be discarded.
- The Junker may also choose to hinder the Mario bros. by incapacitating Luigi. It does this by putting Luigi into a Junker Can. Since this attack cannot be dodged, Mario will be forced to defeat the Junker Can to rescue his brother. However occasionally, Luigi will hit the rim, and escape. If he is not freed, and Mario dies, the player will get a game over, provided he or she has no Retry Clocks.
After the battle, Junker begins to malfunction again, rampaging around and freeing Bowser from captivity in the process. It then destroys itself by running into a locked gate, opening said gate in the process. This allows the Mario bros. to access a pipe connecting Peach's Castle to Pipe Yard.
 Junker X
Junker X is the fifth boss encountered in The Gauntlet. Players are charged 1800 Coins to fight it and the player must beat it in 15 turns or fewer. Compared to Junker, Junker X has higher HP, power, defense and speed, and its attacks are more difficult to evade. Junker X is blue with pink details and its Junker Can Xs are brown with pink eyes.
 Names in Other Languages
||Pun on Hojalata (Tinplate).
||Pun on Basura (Garbage) and Monstruo (Monster). Midbus calls him "robotbasurillo" (a pun on robot and garbage). May also be a reference to the Refrestruo.
||From poubelle (trash) and or (gold).
||Pun on Bidone (Bin) and Automatic
- "Junker" is the only boss outside Bowser's body to be encountered in The Gauntlet, besides Bowser X.
- Midbus calls Junker the "Super Ultra Great Mega Trashy Monster Junker Bot" once again demonstrating his habit of making long and unnecessary names.
- On rare occasions, Luigi will wave to Mario while in one of the Junker Cans. After doing this, the Can's lid will slam on Luigi's hand.