Emeria, the Sky Ruin — ruling 1

Emeria, the Sky Ruin's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless you control seven or more Plains as your upkeep starts, and (2) the ability will do nothing if you control fewer than seven Plains by the time it resolves.

Emeria, the Sky Ruin : règles, fonctionnement et interactions (MTG)

Emeria, the Sky Ruin 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

This land enters tapped. At the beginning of your upkeep, if you control seven or more Plains, you may return target creature card from your graveyard to the battlefield. : Add .

How it works : Emeria, the Sky Ruin

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
Emeria, the Sky Ruin's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless you control seven or more Plains as your upkeep starts, and (2) the ability will do nothing if you control fewer than seven Plains by the time it resolves.
No other card is named in this ruling.