To equip Spiderman with Venom's suit, start the game in "Nightmare" mode. After you defeat the Lizard at the end of round 2, move to the right and fall into the pit where you can find the Lizard's key. Walk through the sewage to the bottom of the ladder, hold Down, and press 2 to make Spider-Man dive into the sewage. Press 2 again, and Spider-Man will leap out wearing Venom's suit.