Leyline of Sanctity

In Commander, Leyline of Sanctity is a narrow but occasionally backbreaking piece of protection — it blanks Nekusar, the Mindrazer wheels, targeted discard from Tinybones, Trinket Thief, and any spell or ability that needs to target you specifically. Outside Commander, it's a Modern and Legacy sideboard staple against Burn and discard-heavy strategies like 8-Rack, where resolving it for free on turn zero ends entire game plans. In Pioneer it sees fringe play as a Burn answer, though the format's lower density of discard effects reduces its ceiling. Vintage has enough broken things happening that Leyline of Sanctity tends to be too narrow for most lists.