EX mode
Finish the game. Then load the cleared saved file, then talk to the old man. The EX mode game has a much higher difficulty setting, with new restrictions in each level.

Alternate costumes
Finish the game first. Then load the cleared saved file. Note: Do not go into EX mode yet. First talk to the costume woman and agree to help her. You will need the item that allows you to leave the maze in order to do this. Talk to the old man to begin EX mode. There are various fabrics that you have to find in the EX mode levels. Take them back to the costume woman to get a new costume. Each character has three different costumes that can be found, based on Street Fighter and Vampire Savior. To get the last costume for each character, beat the Boss on level 100 in EX mode.