You earn them by completing the battles in the Cresselia ex Drop Event. One battle requires one token of Event Stamina , which recharges passively over time or can be replenished with Event Hourglass
While draw power is everywhere in the Pokemon TCG, having an additional draw option as you end your turn can actually be great
If the trainer meets the high additional energy cost of Beast Game GX, and they knock out a foe with it, they can claim up to 4 Prize cards, potentially securing the entire battle in a single turn
The first was in 2016, when the launch of Pokemon Go rocketing Pokemon back into the public consciousness
Sephiroth's detailed card art and incredibly flavorful abilities are hard to beat
Its harder to remove than a mana dork or rock, so its a very powerful piece in any green deck