Lunar Mystic — ruling 1

The triggered ability will go on the stack on top of the instant spell and resolve before it.

Lunar Mystic — ruling 2

The decision to pay {1} is made when the triggered ability resolves. It’s not an additional cost of the instant spell.

Lunar Mystic : règles, fonctionnement et interactions (MTG)

Lunar Mystic 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 cast an instant spell, you may pay . If you do, draw a card.

How it works : Lunar Mystic

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2012· Wizards of the Coast
The triggered ability will go on the stack on top of the instant spell and resolve before it.
No other card is named in this ruling.
#2May 1, 2012· Wizards of the Coast
The decision to pay is made when the triggered ability resolves. It’s not an additional cost of the instant spell.
No other card is named in this ruling.