Leyline of Singularity
Most of the Leyline cycle hands you a static effect a turn early; this one weaponizes the legend rule against the entire board. Making every nonland permanent legendary turns the "no two of the same name" clause into a sweeping symmetry-breaker: opponents can keep one copy of any token, any artifact, any creature, and the rest go to the graveyard the instant a second resolves. Token armies collapse to a single body, Treasure piles cannot coexist, and any deck built on redundant copies of one permanent finds itself capped at one. What complicates the build is that the rule cuts both ways and reads names rather than types, so the controlling player has to field a board of distinctly named permanents, or one wide enough that the legend rule never bites its own side. The free-into-play clause is what makes it a true hate piece rather than a four-mana speed bump, letting it land before the first land drop and pre-empt the strategies it punishes. As a use of the legend rule as a resource it does nothing to the rules text of any single permanent, yet quietly rewrites how an entire archetype is allowed to function.
