A combination of obscene rarity, stellar artwork, usefulness on the tabletop, and a connection to one of MTGs most famous cards have coalesced to drive its price way up
This doesn't just mean retreating - anything that causes the Pokmon to move to the bench causes it to lose any special conditions
You can get up to 27 power and toughness worth of stats just off Kozilek alone, strip cards from your foes' hands, and dig deep into your deck with card draw
Bat- Creature Bat +1/+1 Flying At the beginning of each end step, if an opponent lost 3 or more life this turn, Augment 1B (1B, Reveal this card from your hand: Combine it with target host
What affects the value of Ghoulcaller Gisa
I can easily see it showing up in Ramp decks, Reanimator decks, and everything in between