In terms of gameplay, though, leylines are best known for their iconic ability: "If this card is in your opening hand, you may begin the game with it on the battlefield." Most conventional leylines are four-mana Enchantments, but their opening-hand clause essentially lets you skip out on the cost if you naturally start with one
(5/3/2019) If a permanent leaves the battlefield this way but ends up in a zone other than a library (most likely because it's a player's commander in the Commander variant), it's still counted to determine how many cards to reveal.
Faerie Macabre and Relic of Progenitus are two more frequently played answers and both are around $5 per copy, and those are among the most expensive cards played in the format
You can fill your deck with other pillowfort effects like Ghostly Prison, Propaganda, and Sphere of Safety to make sure you're never attacked again
Understanding how does crew work in MTG starts with grasping one simple concept