I use Dueling Nexus to build my decks because they have the best yugioh deck builder in the world
There is a whole system for determining how rare each card is
In the Phyrexian Praetors: Compleat Edition Secret Lair, there was an incredibly small chance that you could open a serialized Viscera Seer number between 001/100 and 100/100, and the whole of the rest of the card was completely reversed
It was easily a three-of in the casual sixty card decks my friends and I were building
Using the Book of Vile Darkness in combination with the Hand and Eye of Vecna, you can call him forth as an 8/8 indestructible Zombie God who can draw you cards, create Zombie tokens, and buff himself or another creature once per turn
Which is, at the end of the game, when you have to fight your Aeons against Yu Yevons possession