From the Super Mario Wiki
Jailgoons are living cage enemies with a Bowser Minion inside only found in Mario & Luigi: Bowser's Inside Story, in Bowser's Castle.
Jailgoons contain either a Bob-omb or a Goomba imprisioned inside them. These minions are apparently still loyal to Bowser, but have been locked away 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 that heals 30 HP, then promptly flee. If a Jailgoon is defeated by Mario and Luigi, they do not receive a mushroom. 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.
Names in Other Languages
||Pun of Atrapa (Catch) and tórax (thorax).
||From Jaula, which means cage. -ito is an "affection" sufix.
||Cage à bras
||Literally Cage with arms
||Pun on "Sir Lancillotto" (Sir Lancelot) and "cella" (cage)