Made all these group Halloween costumes except for the Joker. The Riddler was the best, was very close to TV quality! and didn’t cost much at all! I bought green dye, white material for belt, white shirt underwear and socks to cover the shoes and thermal pants and dyed them all green. I used cardboard to cut the shape of belt then dyed the white material for the belt purple along with gloves and mask (mask made from head band).
Hot glued material to belt shape and added Velcro to the back. I used black fabric paint to paint on the question marks, printed out the question mark on a piece of paper and cut out with scissors, placed the white part on the shirt for a stencil, not the question mark itself, and filled it in with black marker then with paint. This costume maybe cost $20.
Then for Harley Quinn it was just whatever red and black I could find to put together, added red felt for boot tops, and used an index card and hair clips for the hat. For Poison Ivy took a black swim cover up we found on sale and hot glued Ivy leaves all over the top and bottom, dyed panty hose green and used them for gloves as well. I took an old broken ring and dyed a leaf to it, also took 2 leaves and used adhesive from eye lashes and glued them to corners of the eyes. They were all easy and cheap to make!