In a saucepan over medium heat, combine sweetened condensed milk, cocoa powder, and salted butter. Stir continuously until smooth and slightly thickened (about 5-7 minutes).
Remove from heat and let cool slightly before adding grated chocolate or sprinkles.
Scoop small amounts of the fudge mixture onto a parchment-lined baking sheet and shape into mouse-like bodies.
Press a strawberry onto each fudge body to form the head. Use sliced peanuts for ears.
Decorate with colored sprinkles for eyes and features. Chill in the refrigerator for about 30 minutes before serving.