Echoing Boon — ruling 1

You must name a Magic card. Notably, you can't name a token.

Echoing Boon — ruling 2

If you play multiple games after the draft, you can name a different card in each new game.

Echoing Boon — ruling 3

If an alternative cost was paid for the spell being copied, such as a madness cost or surge cost, the same alternative cost is considered to have been paid for the copy.

Echoing Boon — ruling 4

The instant or sorcery spell can target other things as well, as long as one of its targets is a creature you control with the chosen name.

Echoing Boon — ruling 5

When Echoing Boon's ability resolves, it creates a copy of the instant or sorcery spell. The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger. The copy will then resolve like a normal spell, before the original spell resolves but after players get a chance to cast spells and activate abilities.

Echoing Boon — ruling 6

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 you can't choose a new legal target for one of the targets, then it remains unchanged (even if the current target is illegal).

Echoing Boon — ruling 7

If the spell being copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. You can't choose a different one.

Echoing Boon — ruling 8

If the spell being copied has an X whose value was determined as it was cast (like Subterranean Tremors has), the copy will have the same value of X.

Echoing Boon : règles, fonctionnement et interactions (MTG)

Echoing Boon 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

Hidden agenda (Start the game with this conspiracy face down in the command zone and secretly choose a card name. You may turn this conspiracy face up any time and reveal that name.) Whenever you cast an instant or sorcery spell, if it targets a creature you control with the chosen name, you may copy that spell and may choose new targets for the copy.

How it works : Echoing Boon

Original English text — Wizards of the Coast / Scryfall

#1August 23, 2016· Wizards of the Coast
You must name a Magic card. Notably, you can't name a token.
No other card is named in this ruling.
#2August 23, 2016· Wizards of the Coast
If you play multiple games after the draft, you can name a different card in each new game.
No other card is named in this ruling.
#3August 23, 2016· Wizards of the Coast
If an alternative cost was paid for the spell being copied, such as a madness cost or surge cost, the same alternative cost is considered to have been paid for the copy.
No other card is named in this ruling.
#4August 23, 2016· Wizards of the Coast
The instant or sorcery spell can target other things as well, as long as one of its targets is a creature you control with the chosen name.
No other card is named in this ruling.
#5August 23, 2016· Wizards of the Coast
When Echoing Boon's ability resolves, it creates a copy of the instant or sorcery spell. The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger. The copy will then resolve like a normal spell, before the original spell resolves but after players get a chance to cast spells and activate abilities.
No other card is named in this ruling.
#6August 23, 2016· 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 you can't choose a new legal target for one of the targets, then it remains unchanged (even if the current target is illegal).
No other card is named in this ruling.
#7August 23, 2016· Wizards of the Coast
If the spell being copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. You can't choose a different one.
No other card is named in this ruling.
#8August 23, 2016· Wizards of the Coast
If the spell being copied has an X whose value was determined as it was cast (like Subterranean Tremors has), the copy will have the same value of X.
No other card is named in this ruling.
#9August 23, 2016· Wizards of the Coast
If the spell being copied has damage divided as it was cast, the division can't be changed (although the targets receiving that damage still can).
No other card is named in this ruling.
#10August 23, 2016· Wizards of the Coast
Conspiracies are never put into your deck. Instead, you put any number of conspiracies from your card pool into the command zone as the game begins. These conspiracies are face up unless they have hidden agenda, in which case they begin the game face down.
No other card is named in this ruling.
#11August 23, 2016· Wizards of the Coast
A conspiracy doesn't count as a card in your deck for purposes of meeting minimum deck size requirements. (In most drafts, the minimum deck size is 40 cards.)
No other card is named in this ruling.
#12August 23, 2016· Wizards of the Coast
You don't have to play with any conspiracy you draft. However, you have only one opportunity to put conspiracies into the command zone, as the game begins. You can't put conspiracies into the command zone after this point.
No other card is named in this ruling.
#13August 23, 2016· Wizards of the Coast
You can look at any player's face-up conspiracies at any time. You'll also know how many face-down conspiracies a player has in the command zone, although you won't know what they are.
No other card is named in this ruling.
#14August 23, 2016· Wizards of the Coast
A conspiracy's static and triggered abilities function as long as that conspiracy is face-up in the command zone.
No other card is named in this ruling.
#15August 23, 2016· Wizards of the Coast
Conspiracies are colorless, have no mana cost, and can't be cast as spells.
No other card is named in this ruling.
#16August 23, 2016· Wizards of the Coast
Conspiracies aren't legal for any sanctioned Constructed format, but may be included in other Limited formats, such as Cube Draft.
No other card is named in this ruling.
#17August 23, 2016· Wizards of the Coast
You name the card as the game begins, as you put the conspiracy into the command zone, not as you turn the face-down conspiracy face up.
No other card is named in this ruling.
#18August 23, 2016· Wizards of the Coast
There are several ways to secretly name a card, including writing the name on a piece of paper that's kept with the face-down conspiracy. If you have multiple face-down conspiracies, you may name a different card for each one. It's important that each named card is clearly associated with only one of the conspiracies.
No other card is named in this ruling.
#19August 23, 2016· Wizards of the Coast
As a special action, you may turn a face-down conspiracy face up. You may do so any time you have priority. This action doesn't use the stack and can't be responded to. Once face up, the named card is revealed and the conspiracy's abilities will affect the game.
No other card is named in this ruling.
#20August 23, 2016· Wizards of the Coast
At the end of the game, you must reveal any face-down conspiracies you own in the command zone to all players.
No other card is named in this ruling.
#21August 23, 2016· Wizards of the Coast
A conspiracy with hidden agenda that has a triggered ability must be face up before that ability's trigger condition is met in order for it to trigger. Turning it face up afterward won't have any effect.
No other card is named in this ruling.
#22August 23, 2016· Wizards of the Coast
At the end of the game, you must reveal any face-down conspiracies you own in the command zone to all players. Notably, you can't bluff conspiracies with hidden agenda by putting other cards into the command zone face down as the game starts.
No other card is named in this ruling.