First strike
Whenever Mirri, Weatherlight Duelist attacks, each opponent can't block with more than one creature this combat.
As long as Mirri, Weatherlight Duelist is tapped, no more than one creature can attack you each combat.
Tapping Mirri after creatures have attacked will not remove creatures from combat.
While Mirri is tapped, there’s no restriction on how many creatures can attack planeswalkers you control.