Grenzo's Ruffians — ruling 1

You determine the size of the bonus as the melee ability resolves. Count each opponent that you attacked with one or more creatures. It doesn’t matter if the attacking creatures are still attacking or even if they are still on the battlefield. It also doesn’t matter if the opponent you attacked is still in the game.

Grenzo's Ruffians — ruling 2

It doesn’t matter how many creatures you attacked a player with, only that you attacked a player with at least one creature. For example, if you attack one player with Wings of the Guard and another player with five creatures, Wings of the Guard will get +2/+2 until end of turn.

Grenzo's Ruffians — ruling 3

Melee will trigger if the creature with melee attacks a planeswalker. However, the effect counts only opponents (and not planeswalkers) that you attacked with a creature when determining the bonus.

Grenzo's Ruffians — ruling 4

Creatures that enter the battlefield attacking were never declared as attackers, so they won’t count toward melee’s effect. Similarly, if a creature with melee enters the battlefield attacking, melee won’t trigger.

Grenzo's Ruffians : règles, fonctionnement et interactions (MTG)

Grenzo's Ruffians 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

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.) Whenever this creature deals combat damage to an opponent, it deals that much damage to each other opponent.

How it works : Grenzo's Ruffians

Original English text — Wizards of the Coast / Scryfall

#1August 23, 2016· Wizards of the Coast
You determine the size of the bonus as the melee ability resolves. Count each opponent that you attacked with one or more creatures. It doesn’t matter if the attacking creatures are still attacking or even if they are still on the battlefield. It also doesn’t matter if the opponent you attacked is still in the game.
No other card is named in this ruling.
#2August 23, 2016· Wizards of the Coast
It doesn’t matter how many creatures you attacked a player with, only that you attacked a player with at least one creature. For example, if you attack one player with Wings of the Guard and another player with five creatures, Wings of the Guard will get +2/+2 until end of turn.
No other card is named in this ruling.
#3August 23, 2016· Wizards of the Coast
Melee will trigger if the creature with melee attacks a planeswalker. However, the effect counts only opponents (and not planeswalkers) that you attacked with a creature when determining the bonus.
No other card is named in this ruling.
#4August 23, 2016· Wizards of the Coast
Creatures that enter the battlefield attacking were never declared as attackers, so they won’t count toward melee’s effect. Similarly, if a creature with melee enters the battlefield attacking, melee won’t trigger.
No other card is named in this ruling.