Line bottom and sides of 13x9-inch pan with foil, leaving 1 inch of foil overhanging at 2 opposite sides of pan; grease foil with butter. In medium bowl, stir peanut butter and powdered sugar until well blended. Shape into 24 (1-inch) balls. Place balls evenly in foil-lined pan.
In 5- to 6-quart saucepan, cook butter, granulated sugar and evaporated milk over medium-high heat, stirring constantly, until sugar is dissolved. Heat to full boil, stirring constantly. Reduce heat to medium. Boil uncovered without stirring 3 minutes. Remove from heat.
Stir in 3 cups of the marshmallows until melted. Add chocolate chips, sweet chocolate and unsweetened chocolate, stirring rapidly until all chocolate is melted and mixture is smooth. Stir in vanilla. Quickly pour mixture over peanut butter balls in pan. Press peanuts and remaining marshmallows into top of fudge. Cool completely, about 1 1/2 hours.
Using foil handles, lift fudge from pan to cutting board; remove foil from sides of fudge. Cut into 8 rows by 6 rows.