Regna's Sanction — ruling 1

When Regna’s Sanction resolves and your foes perform their actions, first the next foe in turn order (or, if it’s a foe’s turn, that foe) chooses an untapped creature they control, then each other foe in turn order does the same, then all other creatures those players control are tapped at the same time. Foes will know choices made by earlier players when making their choices.

Regna's Sanction — ruling 2

You make this choice for yourself as well as each other player. In some rare cases, you may wish to call yourself (or your teammate in a Two-Headed Giant game) a foe. You can do that.

Regna's Sanction — ruling 3

The designation of friend or foe is only relevant to the spell that asks you to choose. A player you call your friend doesn’t become your teammate, and the next “friend or foe” spell you cast could name that player your foe.

Regna's Sanction — ruling 4

You may call a player a friend or a foe even if that player will be instructed to perform an impossible action. For example, for Regna’s Sanction, a foe may control no untapped creatures.

Regna's Sanction — ruling 5

Friends perform their specified actions before foes. This means that a friend’s action may cause a triggered ability of a foe’s permanent to trigger before that foe’s action causes that permanent to leave the battlefield.

Regna's Sanction — ruling 6

Players can’t take actions in between the time that friends perform their actions and the time that foes perform theirs. If any abilities trigger from friends performing actions, those triggers won’t be put onto the stack until the foes perform their actions and the spell finishes resolving.

Regna's Sanction : règles, fonctionnement et interactions (MTG)

Regna's Sanction 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

For each player, choose friend or foe. Each friend puts a +1/+1 counter on each creature they control. Each foe chooses one untapped creature they control, then taps the rest.

How it works : Regna's Sanction

Original English text — Wizards of the Coast / Scryfall

#1June 8, 2018· Wizards of the Coast
When Regna’s Sanction resolves and your foes perform their actions, first the next foe in turn order (or, if it’s a foe’s turn, that foe) chooses an untapped creature they control, then each other foe in turn order does the same, then all other creatures those players control are tapped at the same time. Foes will know choices made by earlier players when making their choices.
No other card is named in this ruling.
#2June 8, 2018· Wizards of the Coast
You make this choice for yourself as well as each other player. In some rare cases, you may wish to call yourself (or your teammate in a Two-Headed Giant game) a foe. You can do that.
No other card is named in this ruling.
#3June 8, 2018· Wizards of the Coast
The designation of friend or foe is only relevant to the spell that asks you to choose. A player you call your friend doesn’t become your teammate, and the next “friend or foe” spell you cast could name that player your foe.
No other card is named in this ruling.
#4June 8, 2018· Wizards of the Coast
You may call a player a friend or a foe even if that player will be instructed to perform an impossible action. For example, for Regna’s Sanction, a foe may control no untapped creatures.
No other card is named in this ruling.
#5June 8, 2018· Wizards of the Coast
Friends perform their specified actions before foes. This means that a friend’s action may cause a triggered ability of a foe’s permanent to trigger before that foe’s action causes that permanent to leave the battlefield.
No other card is named in this ruling.
#6June 8, 2018· Wizards of the Coast
Players can’t take actions in between the time that friends perform their actions and the time that foes perform theirs. If any abilities trigger from friends performing actions, those triggers won’t be put onto the stack until the foes perform their actions and the spell finishes resolving.
No other card is named in this ruling.