In a bowl, beat cream cheese, pumpkin and pineapple. Stir in cheddar cheese, beef and onion. Shape into a ball; wrap in plastic. Wrap cheeseball in 4 pieces of string or 4 rubber bands, creating indentions to resemble a pumpkin. Chill 1 hour. Carefully unwrap cheese ball and set it on a platter. Remove stem from the green pepper; add to cheese ball to serve as a pumpkin stem. Slice remaining pepper. Serve with crackers, sliced pepper and assorted vegetables.