Zola a huge marshmallow gun in Lucrezia's secret lab. While mostly harmless, it is impressive looking, and she manages to kill Professor Diaz with it (wielded as a club) before Doctor Mittelmind uses his built-in pulse cannon to make it blow up in Zola's hand.
That Professor Mezzasalma already knew it was a marshmallow gun when the minions reached him implies that Zola tried at first to shoot them with it. Zola not realizing that it was non-lethal (if used as a gun anyway) has cast some doubt on just how much reliable access she has to the memories of her "captive" copy of Lucrezia.
The Marshmallow Gun may have been created as a lure for escaping prisoners, causing them to "arm" themselves with an imposing but useless weapon, rather than something dangerous. However, it can still be used as a club.
It must be said though that it makes a great edible, biodegradable improvement over the nerf guns of our universe. Perhaps it was created to make putting marshmallows into your hot chocolate not only tasty, but a real sporting challenge.