Leyline of Lifeforce — ruling 1

A player's "opening hand" is the hand of cards the player has after all players have taken mulligans. If players have any cards in hand that allow actions to be taken with them from a player's opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.

Leyline of Lifeforce : règles, fonctionnement et interactions (MTG)

Leyline of Lifeforce 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

If this card is in your opening hand, you may begin the game with it on the battlefield. Creature spells can't be countered.

How it works : Leyline of Lifeforce

Original English text — Wizards of the Coast / Scryfall

#1March 19, 2021· Wizards of the Coast
A player's "opening hand" is the hand of cards the player has after all players have taken mulligans. If players have any cards in hand that allow actions to be taken with them from a player's opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.
No other card is named in this ruling.