Magmatic Insight — ruling 1

You must discard exactly one land card to cast Magmatic Insight. You can't cast it without discarding a land card, and you can't discard additional cards.

Magmatic Insight : règles, fonctionnement et interactions (MTG)

Magmatic Insight 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

As an additional cost to cast this spell, discard a land card. Draw two cards.

How it works : Magmatic Insight

Original English text — Wizards of the Coast / Scryfall

#1June 22, 2015· Wizards of the Coast
You must discard exactly one land card to cast Magmatic Insight. You can't cast it without discarding a land card, and you can't discard additional cards.
No other card is named in this ruling.