This could be for a number of reasons
I'm the author of the gaming history book Video Game of the Year: A Year-by-Year Guide to the Best, Boldest, and Most Bizarre Games from Every Year Since 1977 , and the reason everything you know about Street Sharks is a lie
As this mana is green, a Shizuko deck may include spells that allow you to benefit from it more than opponents, such as Helix Pinnacle
While minor differences may exist between individual cards, the condition will be consistent with what is shown in the images
There is, of course, the chance that the packs could contain a valuable card, but its not high, and no better than just buying the packs themselves for their actual price
You can take a look at our Pokemon TCG Database to see an estimated value of each card