Some costume ideas that use spandex body suits include Spiderman, a skeleton, a Power Ranger and Slim Goodbody. Some others are Batgirl, Harley Quinn, and Thing 1 or Thing 2 from "The Cat In The Hat."
For a Spiderman costume, use puffy fabric paint to draw web designs on a red or blue spandex body suit. Allow the paint to dry fully before wearing the suit. Add a Spiderman mask and red boots. To make a skeleton costume, start with a black or grey body suit and carefully paint a skeleton on the front of it using acrylic paint. Alternatively, you can cut bone shapes out of sticker paper and place them onto the suit. For a Slim Goodbody costume, use a white or beige body suit and paint or draw the various organs of the body on the front of it.
To make a Thing 1 or Thing 2 costume, make a circular label that reads "Thing 1" or "Thing 2" and attach it to the front of a red spandex body suit. Wear red shoes or slippers along with a blue wig to complete the look. You can also recreate most superhero costumes using a body suit as a starting point.