Like most Pokmon cards, the value of Shaymin depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Destined Rivals)
It also opens the door to the likes of Farseek, Sylvan Scrying, and Kodama's Reach
Given that the majority of decks play a single ink per turn this effectively turns it from a turn 2 play into a turn 3 play, giving players an extra turn before Bucky comes in and starts coming after your hand of cards
Its an extremely cheap card to summon, costing only one forest mana to get onto the field, and it can be great as a way to get resources onto the field
However, this deck does have Tashigi, Hina, and Helmeppo, 3 cards that have seen play throughout different metas
[56] Pokmon Crystal was received well by critics, although many commented that there were just not enough new additions and features to significantly set it apart from Pokmon Gold and Silver