Jolrael, Voice of Zhalfir — ruling 1

Use the number of cards in your hand as Jolrael's first ability resolves to determine the value of X. Once the ability resolves, that value is locked in. The power and toughness of the land creature won't change if the number of cards in your hand changes later in the turn.

Jolrael, Voice of Zhalfir — ruling 2

Jolrael's last ability applies to any land creature you control that deals combat damage to a player, not only lands that become land creatures because of Jolrael's first ability.

Jolrael, Voice of Zhalfir : règles, fonctionnement et interactions (MTG)

Jolrael, Voice of Zhalfir 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

At the beginning of combat on your turn, up to one target land you control becomes an X/X green and blue Bird creature with flying and haste until end of turn, where X is the number of cards in your hand. It's still a land. Whenever a land creature you control deals combat damage to a player, draw a card.

How it works : Jolrael, Voice of Zhalfir

Original English text — Wizards of the Coast / Scryfall

#1May 12, 2023· Wizards of the Coast
Use the number of cards in your hand as Jolrael's first ability resolves to determine the value of X. Once the ability resolves, that value is locked in. The power and toughness of the land creature won't change if the number of cards in your hand changes later in the turn.
No other card is named in this ruling.
#2May 12, 2023· Wizards of the Coast
Jolrael's last ability applies to any land creature you control that deals combat damage to a player, not only lands that become land creatures because of Jolrael's first ability.
No other card is named in this ruling.