My son wanted a super hero party for his 6th birthday. We decorated a large room with lots of cartoon sound effects by cutting out colored poster board and words such as BAM! and POW! and placing them around the room.  We also had lots of star-shaped balloons. Behind the cake table, I opened and flattened a refrigerator box and cut the top of the box to resemble a city skyline.  I painted this skyline black and used chalk to color in some lighted windows.  Over the skyline, I placed a homemade Bat Signal. On the invitations, we asked everyone to dress up, but we also had costumes available at the party. We bought several plastic tablecloths at the dollar store and made four capes from each tablecloth.  We also bought masks and costume jewelry rings. For games, we had lock up the bad guy.  This is a version of pin the tail on the donkey, but we took a clip art picture of a prison in the traditional striped uniform and enlarged it, glued the picture to a piece of posterboard and drew a jail cell over him. The kids were blindfolded and given a key that they had to pin in the lock. We also had pictures of various "bad guys" on balloons and the heroes had to "get" the bad guys by stomping on the balloons.  Mostly, the kids just had free play time at this party and let their imaginations run wild.