Change the size of characters (Neo Geo CD): During a fight, pause the game. By pressing D the characters will be tiny, small with C, just a little smaller than normal with B, and normal size with A. During a match against the CPU, doing these commands with the unused controller will change its character's size!
Play Duke & Shuko (Neo Geo AES): At the character select screen, put the cursor on the characters in this right order: Billy, Marian, Cheng Fu, Jimmy. Wait for about 3 seconds, and if the tip worked, you will hear 'Bingo!'