Hey every one I was able to get tons of victories against Dr.Crowler using these 3 cards: 1.Gravekeepers Vassal 2.Union Attack 3.Secret Pass to the Treasures They way I used these cards is that I made sure that I had two powerful monsters on the field that attack points were 2500-4000 before I summoned Gravekeepers Vassal then I used Secret Pass to the Treasures first before I used Union Attack because if you do Gravekeepers Vassal only have 700 attack points if you do use Secret Pass to the Treasures it can attack your opponent directly but before you attack I suggest that you use two Union Attack spell cards on Gravekeepers Vassal so it will gain the attack points of the two other monsters on the field twice then attack your opponent directly and you win the duel. I hope this advice will help people who don't have Dr.Crowler unlocked yet.