Its sort of the game designer's way of signaling, Hey, this card is important! Every new set of cards that comes out takes place in a different world (called planes), so the legends of each plane tend to pop up whenever a new set comes out in a plane the game has already visited
Deny the Witch This four-cast instant costs three colors of mana but is very strong with the ability to counter any spell or activity and then force that person to lose some life
Its also another card that you can find for a much more reasonable price with different variants as low as $10 if the collectability or alternate art variant isnt important to you
Phasing out an opponent's creature before they do something busted like a combo buys some breathing room to find a proper answer
Seriously, you do not have to sell me very hard on "play a blue card that tutors for a bunch of things." For those of you who wish I would get back to talking about real decks, dont worry
The Earth Crystal is a counter doubler, and cost reduction, at four mana