Executioner's Swing — ruling 1

You can’t choose a creature that hasn’t yet dealt damage during the turn as the target of Executioner’s Swing, so in most cases it’s not possible for Executioner’s Swing to reduce the amount of combat damage a creature deals. (If a creature has double strike, you could cast Executioner’s Swing after it deals first-strike damage but before it deals regular combat damage.)

Executioner's Swing — ruling 2

It doesn’t matter what the creature dealt damage to or if that damage was combat damage.

Executioner's Swing : règles, fonctionnement et interactions (MTG)

Executioner's Swing is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Target creature that dealt damage this turn gets -5/-5 until end of turn.

How it works : Executioner's Swing

Original English text — Wizards of the Coast / Scryfall

#1January 24, 2013· Wizards of the Coast
You can’t choose a creature that hasn’t yet dealt damage during the turn as the target of Executioner’s Swing, so in most cases it’s not possible for Executioner’s Swing to reduce the amount of combat damage a creature deals. (If a creature has double strike, you could cast Executioner’s Swing after it deals first-strike damage but before it deals regular combat damage.)
No other card is named in this ruling.
#2January 24, 2013· Wizards of the Coast
It doesn’t matter what the creature dealt damage to or if that damage was combat damage.
No other card is named in this ruling.