Certain in-game enemies are only able to be fought by Mario & Luigi or Bowser. Despite this, a few Bowser-oriented enemies have unique behaviors for Mario & Luigi, which can only be seen through hacking the game:

• All of Naplock's attacks can be dodged or countered by jumping, with its snot bubble attack also missing Mario & Luigi entirely even if nothing is done.
• Dark Mechawful's punch attack can be countered with Mario & Luigi's hammers, while its countdown attack is replaced by the same star attack used by the Dark Mechawful head, which can fight Mario & Luigi in normal gameplay if Bowser inhales it. However, in a hacked Dark Mechawful fight, this attack progresses extremely slowly.
• The smoke signals at the start of Choomba's charge attack are changed from fist and shell icons to "M" and "L" ones, indicating which brothers it will charge at and in which order; the attack can also be countered by hammering.
• Dark Trashure's thrown items can be avoided or countered by jumping, similarly to its standard counterpart. However, the items move far faster than those thrown by a regular Trashure or a Dark Trashure fought by Bowser.

While most of these behaviors appear to be failsafes, Choomba is unique in that the "M" and "L" smoke signals are not present anywhere else in the game, indicating that at one point in development, Mario & Luigi would've been able to explore the Tunnel, where Choombas are fought.

Meanwhile, when hacking the game to allow Bowser to fight enemies that can only be encountered by Mario & Luigi, most of them will either crash the game, flee immediately, or display glitchy behavior. One unique case is Magifoofas, which can be inhaled by Bowser (despite the Vacuum Block not indicating this), indicating that the developers considered letting him encounter them in some form.