Start morphed
Press Up, Down, Left, Right, X, B, Y, A, Start at the title screen. The text on the screen will turn blue to confirm correct code entry.
Double morph
Begin a two player game and allow one player to collect all the power-ups until the corresponding morph meter is full. Wait until the other player's pink life bar is almost empty. When the first player morphs, the second player will do so as well.