Heck, theres a Kingdra ex from Shrouded Fable that does 50 damage per Water Energy attached, where its fairly simple to get six Energy on board
"Population reports are the single most important tool for evaluating the true rarity of a graded card
From memory Shadowspear was around five USD the first few weeks after THB released Because of its relevance in the Theros story arc, I think were mainly going to see it getting reprinted in supplemental sets or universes beyond sets because reprinting it in Amonkhet or Lorwyn would make little sense
Secret Rares, full arts, and alternate arts from special sets often hold the highest value
Juju Bubble Juju Bubble is notoriously bad, and its also infamously common in older collections
Others focused entirely on countering it, but, either way, Zoroark came to dictate the game