The company decides how hard it is to find the rare card.

Also, the harder the difficulty in Challenge, the higher the chance of getting a rare card from the game.

The cards, rare until the early 1980's, will be used for an estimated $6 billion in calls this year.

A common strategy is to save rare cards for the right moment.

"A rare card that was worth $20 in 1978 is now worth $30,000," he said.

This attribute measures how rare the card is within the overall distribution of the game.

Weapons - Relatively rare cards which depict a weapon of some type.

Each pack included one rare card, three uncommon, and eight common cards.

The price of the rare cards depends as well on market demands.

At the store, rare cards costing $25 or more are kept under glass.