From the Super Mario Wiki
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Jailgoons contain either a Bob-omb or a Goomba imprisoned inside them. These minions are apparently still loyal to Bowser, but have been locked away by Fawful to prevent trouble. It has a cannon and shield for arms. They attack by either shooting cannonballs at the characters with their cannon or ramming into the character with their shield. Bowser can withdraw into his shell to avoid being hit by the cannonball attack. If it attempts to ram him with its shield, he must punch it repeatedly until it backs off, or it will hit him with its cannon. After a Jailgoon is defeated, the minion will break out of the cage and reward Bowser with a Mushroom (a Drumstick in the remake) that heals 30 HP, then promptly flee. If a Jailgoon is defeated by Mario and Luigi, they do not receive a mushroom. The only difference between the Jailgoons is if Bowser breathes fire at a Jailgoon with a Bob-omb inside, then its fuse will be lit and it explodes next turn, taking out the Jailgoon in the process. However, since the captive Bob-omb was destroyed as well, Bowser will not get a mushroom.
In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, in battle, they can blare their sirens to summon another Jailgoon. Furthermore, they no longer shoot cannonballs at Mario and Luigi in the overworld, and only one Jailgoon can be encountered rather than being fought with Magifoofas when battling them.
Mario & Luigi: Bowser's Inside Story / Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
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