Like most Pokmon cards, the value of Mew ex 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 (Celebrations: Classic Collection)
Its cheap, you can split the payment across multiple turns, and any deck can exploit it due to its colorless identity
There are 29 spells in the deck that have X in their mana value, so hitting a few of those and getting the reduction out of the box is going to be mostly consistent
The small patch of grass on Route 7 is a great place to do some training before you take on the Gym Leader in Celadon City
Lx2 Retreat 0 Price History Hover the chart for exact dates and prices
Without it there would be no Pokemon TCG, no E4, no r/pokeinvesting (I could live without this last one)