Mystic Barrier | Estrid's Invocation

Cards

Mystic Barrier and
Estrid's Invocation on the battlefield (
Estrid's Invocation as a copy of
Mystic Barrier).
You have at least two opponents.

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.
As long as there are three or more players in the game, creatures cannot attack.