Xander's Pact — ruling 1

If you cast a spell for another cost “rather than pay its mana cost,” you can't choose to cast it for any alternative costs such as a blitz cost. You can, however, pay additional costs, such as a casualty cost. If the spell has any mandatory additional costs, those must be paid to cast it.

Xander's Pact — ruling 2

If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Xander's Pact — ruling 3

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.”

Xander's Pact — ruling 4

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

Xander's Pact — ruling 5

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

Xander's Pact — ruling 6

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.

Xander's Pact : règles, fonctionnement et interactions (MTG)

Xander's Pact 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 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell.) Each opponent exiles the top card of their library. You may cast spells from among those cards this turn. If you cast a spell this way, pay life equal to that spell's mana value rather than pay its mana cost.

How it works : Xander's Pact

Original English text — Wizards of the Coast / Scryfall

#1April 29, 2022· Wizards of the Coast
If you cast a spell for another cost “rather than pay its mana cost,” you can't choose to cast it for any alternative costs such as a blitz cost. You can, however, pay additional costs, such as a casualty cost. If the spell has any mandatory additional costs, those must be paid to cast it.
No other card is named in this ruling.
#2April 29, 2022· Wizards of the Coast
If a spell has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
No other card is named in this ruling.
#3April 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.
#4April 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.
#5April 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.
#6April 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.