League Guildmage — ruling 1

If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell.

League Guildmage — ruling 2

League Guildmage's second ability can copy any instant or sorcery spell you control, not just one with targets.

League Guildmage — ruling 3

The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger.

League Guildmage — ruling 4

If you copy a spell, you control the copy. It will resolve before the original spell does.

League Guildmage — ruling 5

The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).

League Guildmage — ruling 6

If the spell that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. A different mode can't be chosen.

League Guildmage — ruling 7

If the spell that's copied has an X whose value was determined as it was cast (like Banefire does), the copy will have the same value of X.

League Guildmage — ruling 8

If the spell has damage divided as it was cast, the division can't be changed (although the targets receiving that damage still can). The same is true of spells that distribute counters.

League Guildmage : règles, fonctionnement et interactions (MTG)

League Guildmage 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

, : Draw a card. , : Copy target instant or sorcery spell you control with mana value X. You may choose new targets for the copy.

How it works : League Guildmage

Original English text — Wizards of the Coast / Scryfall

#1October 5, 2018· Wizards of the Coast
If a spell has in its mana cost, include the value chosen for that X when determining the mana value of that spell.
No other card is named in this ruling.
#2October 5, 2018· Wizards of the Coast
League Guildmage's second ability can copy any instant or sorcery spell you control, not just one with targets.
No other card is named in this ruling.
#3October 5, 2018· Wizards of the Coast
The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger.
No other card is named in this ruling.
#4October 5, 2018· Wizards of the Coast
If you copy a spell, you control the copy. It will resolve before the original spell does.
No other card is named in this ruling.
#5October 5, 2018· Wizards of the Coast
The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).
No other card is named in this ruling.
#6October 5, 2018· Wizards of the Coast
If the spell that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. A different mode can't be chosen.
No other card is named in this ruling.
#7October 5, 2018· Wizards of the Coast
If the spell that's copied has an X whose value was determined as it was cast (like Banefire does), the copy will have the same value of X.
No other card is named in this ruling.
#8October 5, 2018· Wizards of the Coast
If the spell has damage divided as it was cast, the division can't be changed (although the targets receiving that damage still can). The same is true of spells that distribute counters.
No other card is named in this ruling.
#9October 5, 2018· Wizards of the Coast
The controller of a copy can't choose to pay any alternative or additional costs for the copy. However, effects based on any alternative or additional costs that were paid for the original spell are copied as though those same costs were paid for the copy.
No other card is named in this ruling.