It's definitely the 'Hot E-Tank Mod' they left in, and are waiting to see if anyone else besides me could crack it. When battling Splash Woman, she will offer you an E-Tank if you enter her chamber with one bar of life, 6 E-Tanks and 9 lives. The scene will automatically move to Plug Man's stage where he will plug himself into an outlet in his boss room. A special cutscene video ensues on the jumbotron involving Rock and Splashy. Didn't you guys wonder why the screen was always fuzzy?
AO-lawsuits will ensue, but Capcom doesn't care because they need the pub. Yet they will make more money from horny nerds buying the game, wanting to see this secret, that Legends 3 is fully funded through it. Go try it out.