Gwendolyn, Herald of Peace

This spell cannot be countered
During your untap step, you may choose
to not untap Gwendolyn, Herald of Peace
While Gwendolyn, Herald of Peace is untapped,
all other creatures you control have first strike,
and opponents' creatures can't gain, and lose
first strike.
While Gwendolyn, Herald of Peace is tapped,
all other creatures you control have vigilance.