I would go with some sort of extension of Oktoberfest, with a assortment of rides.
Rides:
Black Forest's Phantom: a wooden rollercoaster that goes into the heart of the forest, with pines and caves to go near and at times through.
Der Kegs: a flat ride, with "kegs" spinning by hand pushing
Alpine Blitzkrieg: a alpine slide, on a "mountain" filled with snowy caves, and lush rivers flowing down the alps.
Restaurants:
Hofbrauhaus: German cuisine, festive music, & bier garten seating available.
Red Riding hoods goodies: a pretzel shop
Stores:
Berlin's market: German themed goods, clothing, gifts, and toys!