Nerve Scalpel

Once per Turn Action -

: Attack. Go again

Piercing 1

When this hits a hero, the next time they defend with 1 or more reaction cards this turn, those cards get -1

while defending.

Rulings

From the Outsiders release notes

Reaction cards include both defense reactions and attack reactions.
If two or more attack reactions are declared as defending cards at once, they would all get -1.
If two or more defense reactions are played, they would not all get -1 because each defense reaction must be resolved one at a time, and the first that resolves (and thus defends) would count as the next time, and get the -1.
If a hero is hit two or more times by Nerve Scalpel and has not yet defended, the effects stack and the next time they defend with 1 or more reaction cards this turn, those cards have -1 for each time they were hit by a Nerve Scalpel this turn.
If a hero is hit by Nerve Scalpel after a defense reaction is played, but before it resolves, then that defense reaction will get -1 after it resolves and becomes defending.

Keyword notes

Piercing X - If this is defended by an equipment, it has +X{p}.

Piercing X is a static ability that generates a continuous effect.
If an attack with Piercing is defended by multiple equipment, it does not gain +X for each defending equipment.
If an attack has multiple instances of Piercing X, each effect is evaluated and applied separately.
If an attack with Piercing is no longer defended by an equipment, it loses its +X bonus.