Dina, Soul Steeper — ruling 1

X is the power the creature had when it was on the battlefield, not the power it has in the graveyard.

Dina, Soul Steeper — ruling 2

Each creature with lifelink dealing combat damage causes a separate life gain event. For example, if two creatures you control with lifelink deal combat damage at the same time, a "whenever you gain life" ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.

Dina, Soul Steeper — ruling 3

When Dina's first ability resolves, each opponent loses only 1 life, no matter how much life was gained.

Dina, Soul Steeper — ruling 4

Dina's first ability triggers only once for each life gain event, no matter how much life was gained.

Dina, Soul Steeper : règles, fonctionnement et interactions (MTG)

Dina, Soul Steeper 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

Whenever you gain life, each opponent loses 1 life. , Sacrifice another creature: Dina gets +X/+0 until end of turn, where X is the sacrificed creature's power.

How it works : Dina, Soul Steeper

Original English text — Wizards of the Coast / Scryfall

#1April 16, 2021· Wizards of the Coast
X is the power the creature had when it was on the battlefield, not the power it has in the graveyard.
No other card is named in this ruling.
#2April 16, 2021· Wizards of the Coast
Each creature with lifelink dealing combat damage causes a separate life gain event. For example, if two creatures you control with lifelink deal combat damage at the same time, a "whenever you gain life" ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.
No other card is named in this ruling.
#3April 16, 2021· Wizards of the Coast
When Dina's first ability resolves, each opponent loses only 1 life, no matter how much life was gained.
No other card is named in this ruling.
#4April 16, 2021· Wizards of the Coast
Dina's first ability triggers only once for each life gain event, no matter how much life was gained.
No other card is named in this ruling.