Cavern isnt a card that youll find spread through many decks, but in tribal decks, its going to be incredibly powerful to shut off opposing counterspells
Pricing cards Since the card economy on MTGO mirrors the paper economy, I would price cards the same way: Find an agreed-upon site to base prices on
You can also tap it and pay four mana, one of which is Green and one of which is White, to add a +1/+1 counter to each Creature you control
These are both pretty expensive cards, but they also very clearly "build arounds." I'm a big fan of Roon of the Hidden Realm because I love being able to blink cards with "enters the battlefield" abilities, and Y'shtola is not only able to blink twice every turn, but she also doubles any other "end of turn" effects that trigger as well
Despite this, I have no interest in watching any of these horror movies