I owned it and go down to 5
Rare cards typically feature a fully evolved, Mythical or Legendary Pokmon
It cant beat mass removal that doesnt destroy or target, so a card like Toxic Deluge will still work
Sure, there are other moist creature types out there, but Merfolk are pretty consistently hard to deal with and incredibly powerful, and what more can you really ask for from a bunch of Creatures that like chilling out on river beds and stuff
Flying types are immune to Ground types, meaning that they receive no damage: Ground - Flying types dont touch the ground, so their attacks cant affect them
Going from a population of 50 to 300 can really crater the value for individual owners of those cards, said Whatnots LaFontaine