Nourishing Shoal — ruling 1

If a card in a player's hand has {X} in its mana cost, X is considered to be 0.

Nourishing Shoal — ruling 2

If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.

Nourishing Shoal : règles, fonctionnement et interactions (MTG)

Nourishing Shoal 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

You may exile a green card with mana value X from your hand rather than pay this spell's mana cost. You gain X life.

How it works : Nourishing Shoal

Original English text — Wizards of the Coast / Scryfall

#1December 7, 2018· Wizards of the Coast
If a card in a player's hand has in its mana cost, X is considered to be 0.
No other card is named in this ruling.
#2December 7, 2018· Wizards of the Coast
If a spell has in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.
No other card is named in this ruling.