The Franklin Badge is from the Earthbound series of games, from Mother 1 to Mother 3. It allows the heroes to reflect certain attacks. It’s been in the Super Smash Bros. series since Brawl.
All you have to do is wear it, and all attacks that are projectiles will bounce off of you. Just like the Fox reflect, but you literally don’t have to do anything.
Which makes it really effective against a lot of characters. You’re safe from giant laser blasts.
But against foes like Donkey Kong, it’s useless, unless Donkey Kong has a good item.