So, like, this guy shoots toast at you. As you can see from the schematics, his nose is the toaster lever thing. His boss fight is a lot like Dust Man, except he absorbs your bullets, toasts them, and then shoots them back at you.
So, when you defeat him, you get the
Toast Slot. If an enemy bullet enters your Mega Buster, it charges up. The power of your shot is a geometrically increasing sum of the bullets (e.g. 1, 2, 4, 8...). You have to shoot within a certain time span though; if you wait too long, the bullets will burn and not deal as much damage.
Toast Shot super-effective against Peanut Butter Jelly Man. His weakness is Fork And Curious Toddler Man.