Grisly Sigil — ruling 1

If you cast Grisly Sigil targeting a creature or planeswalker that hasn't been dealt noncombat damage this turn, choose to pay its casualty cost, and choose not to change the target, the copy will deal 1 damage and you will gain 1 life. Then, the original spell will resolve. It will deal 3 damage, and you will gain 3 life.

Grisly Sigil — ruling 2

Casualty N means “As an additional cost to cast this spell, you may sacrifice a creature with power N or greater.” and “When you cast this spell, if a casualty cost was paid for it, copy it. If the spell has any targets, you may choose new targets for the copy.”

Grisly Sigil — ruling 3

You may sacrifice only one creature to pay a spell's casualty cost, and you copy the spell only once.

Grisly Sigil — ruling 4

If you pay the casualty cost of a spell, the copy will resolve before the original spell.

Grisly Sigil — ruling 5

The copy of the spell is created on the stack, so it's not “cast.” Abilities that trigger when a player casts a spell won't trigger.

Grisly Sigil : règles, fonctionnement et interactions (MTG)

Grisly Sigil 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

Casualty 1 (As you cast this spell, you may sacrifice a creature with power 1 or greater. When you do, copy this spell and you may choose a new target for the copy.) Choose target creature or planeswalker. If it was dealt noncombat damage this turn, Grisly Sigil deals 3 damage to it and you gain 3 life. Otherwise, Grisly Sigil deals 1 damage to it and you gain 1 life.

How it works : Grisly Sigil

Original English text — Wizards of the Coast / Scryfall

#1April 29, 2022· Wizards of the Coast
If you cast Grisly Sigil targeting a creature or planeswalker that hasn't been dealt noncombat damage this turn, choose to pay its casualty cost, and choose not to change the target, the copy will deal 1 damage and you will gain 1 life. Then, the original spell will resolve. It will deal 3 damage, and you will gain 3 life.
No other card is named in this ruling.
#2April 29, 2022· Wizards of the Coast
Casualty N means “As an additional cost to cast this spell, you may sacrifice a creature with power N or greater.” and “When you cast this spell, if a casualty cost was paid for it, copy it. If the spell has any targets, you may choose new targets for the copy.”
No other card is named in this ruling.
#3April 29, 2022· Wizards of the Coast
You may sacrifice only one creature to pay a spell's casualty cost, and you copy the spell only once.
No other card is named in this ruling.
#4April 29, 2022· Wizards of the Coast
If you pay the casualty cost of a spell, the copy will resolve before the original spell.
No other card is named in this ruling.
#5April 29, 2022· Wizards of the Coast
The copy of the spell is created on the stack, so it's not “cast.” Abilities that trigger when a player casts a spell won't trigger.
No other card is named in this ruling.