Valakut, the Molten Pinnacle — ruling 1

You target a permanent or player when the ability triggers. You decide whether to have Valakut deal damage to that permanent or player as the ability resolves.

Valakut, the Molten Pinnacle — ruling 2

If multiple Mountains enter under your control at the same time, Valakut's second ability could trigger that many times. Each ability takes into consideration the other Mountains that entered at the same time as the one that caused it to trigger.

Valakut, the Molten Pinnacle — ruling 3

Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves.

Valakut, the Molten Pinnacle — ruling 4

If a Mountain you control leaves the battlefield between the time Valakut's second ability triggers and the time it resolves, be aware if that was the Mountain that caused Valakut's ability to trigger or not. If it was, Valakut's count isn't affected; if it wasn't, Valakut's count goes down by one.

Valakut, the Molten Pinnacle : règles, fonctionnement et interactions (MTG)

Valakut, the Molten Pinnacle 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. Whenever a Mountain you control enters, if you control at least five other Mountains, you may have this land deal 3 damage to any target. : Add .

How it works : Valakut, the Molten Pinnacle

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
You target a permanent or player when the ability triggers. You decide whether to have Valakut deal damage to that permanent or player as the ability resolves.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
If multiple Mountains enter under your control at the same time, Valakut's second ability could trigger that many times. Each ability takes into consideration the other Mountains that entered at the same time as the one that caused it to trigger.
No other card is named in this ruling.
#3October 1, 2009· Wizards of the Coast
Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves.
No other card is named in this ruling.
#4October 1, 2009· Wizards of the Coast
If a Mountain you control leaves the battlefield between the time Valakut's second ability triggers and the time it resolves, be aware if that was the Mountain that caused Valakut's ability to trigger or not. If it was, Valakut's count isn't affected; if it wasn't, Valakut's count goes down by one.
No other card is named in this ruling.