If it's how I remember it, you get the Marmite from the Clefairy (the thing in the cave shouting about 'Helix), you have to give it the Helix Fossil you can pick up elsewhere. The Konami code thing you're thinking of is actually a play on Twitch Plays Pokemon, it's not actually a code the player needs to punch in anywhere. Thanks for giving this a try btw!