3 mana to counter target spell is fairly mediocre, but the flexibility of being able to turn it into card selection or copying a creature or an artifact makes it pretty good, especially given those kind of copy spells are typically sorceries
Until the end of your next turn, you may play those cards
"Typically when a card is more playable in the TCG community, it does impact the value somewhat
One of mill's weaknesses is that you might enable your opponents' powerful graveyard strategies, so Ashiok, Dream Render alleviates that concern
Often combined with Avenger of Zendikar in a Tooth and Nail entwinement, Craterhoof Behemoth is an object lesson in playing your Fogs
Mastery Pass Speaking of the Mastery Pass, if you're planning to play MTG Arena regularly, investing in this pass can significantly accelerate your card collection process