Jace, Unraveler of Secrets

Oracle Text

+1: Scry 1, then draw a card.

−2: Return target creature to its owner's hand.

−8: You get an emblem with "Whenever an opponent casts their first spell each turn, counter that spell."

Card Rulings

4/8/2016 The emblem’s triggered ability counters the first spell an opponent casts on each turn, not just that opponent’s turn.
4/8/2016 If Jace’s emblem’s triggered ability doesn’t counter the first spell an opponent casts (perhaps because that spell can’t be countered), it won’t trigger again in the same turn to try to counter that player’s second spell.
4/8/2016 If you have multiple opponents, Jace’s emblem can trigger once each turn for each opponent.