Frontier Explorer — ruling 1

In a casual game, a card you choose from outside the game comes from your personal collection. In a tournament event, a card you choose from outside the game must come from your sideboard, which includes an arbitrary number of basic lands. You may look at your sideboard at any time.

Frontier Explorer : règles, fonctionnement et interactions (MTG)

Frontier Explorer 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

, : Until end of turn, you may play one basic Plains card from outside the game.

How it works : Frontier Explorer

Original English text — Wizards of the Coast / Scryfall

#1November 12, 2019· Wizards of the Coast
In a casual game, a card you choose from outside the game comes from your personal collection. In a tournament event, a card you choose from outside the game must come from your sideboard, which includes an arbitrary number of basic lands. You may look at your sideboard at any time.
No other card is named in this ruling.