Mystic Barrier + Estrid's Invocation

Mystic Barrier

Estrid's Invocation

How it works

1. At the beginning of each of your upkeeps, Mystic Barrier and Estrid's Invocation trigger, choosing "left" for Mystic Barrier and "right" for Estrid's Invocation.
2. As long as there are three or more players in the game, creatures cannot attack.

By casting Mystic Barrier, you establish a directional restriction that dictates which player and planeswalkers can be attacked. We can bypass this restriction's choice at the beginning of each upkeep by bringing in Estrid's Invocation as a copy of Mystic Barrier. Because Estrid's Invocation allows us to choose a different direction—such as "right" while the original points "left"—the overlapping restrictions mean no opponent qualifies as the nearest valid target in both directions simultaneously when three or more players remain in the game. This creates a complete combat lock where creatures can no longer attack at all.