Geometer's Arthropod — ruling 1

In some rare cases, the value of X for the spell on the stack may be different than the value that was chosen when you cast it. For example, if you control Unbound Flourishing (an enchantment with "Whenever you cast a permanent spell with a mana cost that contains {X}, double the value of X.") the value of X may have been doubled. In those cases, use the value of X as the spell exists on the stack at the time Geometer's Arthropod's ability resolves to determine the value of X for Geometer's Arthropod's ability.

Geometer's Arthropod — ruling 2

Geometer's Arthropod's ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving. In that case, use the value of X as that spell last existed on the stack to determine the value of X for Geometer's Arthropod's ability.

Geometer's Arthropod : règles, fonctionnement et interactions (MTG)

Geometer's Arthropod 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 a spell with in its mana cost, look at the top X cards of your library. Put one of them into your hand and the rest on the bottom of your library in a random order.

How it works : Geometer's Arthropod

Original English text — Wizards of the Coast / Scryfall

#1March 20, 2026· Wizards of the Coast
In some rare cases, the value of X for the spell on the stack may be different than the value that was chosen when you cast it. For example, if you control Unbound Flourishing (an enchantment with "Whenever you cast a permanent spell with a mana cost that contains , double the value of X.") the value of X may have been doubled. In those cases, use the value of X as the spell exists on the stack at the time Geometer's Arthropod's ability resolves to determine the value of X for Geometer's Arthropod's ability.
No other card is named in this ruling.
#2March 20, 2026· Wizards of the Coast
Geometer's Arthropod's ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving. In that case, use the value of X as that spell last existed on the stack to determine the value of X for Geometer's Arthropod's ability.
No other card is named in this ruling.