When an effect resolves that was activated by your opponent's Effect Monster on the field, they can discard 1 card. If they do not, that effect is negated.
Near Mint Unlimited - $1.90
Near Mint 1st Edition - $2.70
Lightly Played Unlimited - $1.60
Lightly Played 1st Edition - $2.20
Moderately Played Unlimited - $1.30
Moderately Played 1st Edition - $1.80
Heavily Played Unlimited - $1.00
Heavily Played 1st Edition - $1.40