Instructions
Defeat Marik, leader of the Ghouls and boss of the game, at the Pyramid. He is one of the most difficult opponents you'll face up to that point. If you continue to lose this duel, you'll need more experience or a better deck.
Take part in the newest available tournament and win it.
Play all four subsequent limited tournaments and win these as well, thereby winning all limited tournaments in the game.
Look in your trunk. The Gate Guardian and his pieces should appear automatically as soon as you win the last tournament.