mtg cards with x in the casting cost What does mana mean Magic the Gathering? Mana Cost: humanReadable.~[x], 11 cards

While you're limited by the mana value, there are tons of options for terrifying, cheap Auras like All That Glitters and Twinblade Blessing

(The exception on rarity are those serialized reprints of cards that are intentionally limited before printing)

Rewind Rewind is perhaps the worst free counterspell you can play since it requires mana upfront, and I find it generally unimpressive, but it has its uses

There are 7 rare (less than 1%) and 3 mythic rare (less than 1%) web-slinger cards that can be found in this slot

Its a great early pick because it goes in any blue deck, and then it plays perfectly into your game of discarding threats while looking for reanimation spells