Crush 40 wafers to form fine crumbs; place in medium bowl.
Add 1/4 cup butter and 2 Tbsp. sugar; mix well. Press onto bottom and up side of 9-inch pie plate. Coarsely crush remaining wafers; mix with remaining butter. Reserve for later use.
Beat all remaining ingredients except marshmallows with mixer until well blended; pour into crust.
Bake 50 to 55 min. or until knife inserted in center comes out clean. Top with crumb mixture and marshmallows; bake 5 min. or until marshmallows are puffed. Cool completely. Refrigerate until ready to serve.