Through the Breach — ruling 1

If all of the spell’s targets are illegal when the spell tries to resolve, it won’t resolve and none of its effects will happen.

Through the Breach — ruling 2

You reveal all cards you intend to splice at the same time. Each individual card can be spliced only once onto any one spell.

Through the Breach — ruling 3

A card with a splice ability can’t be spliced onto itself because the spell is on the stack (and not in your hand) when you reveal the cards you want to splice onto it.

Through the Breach — ruling 4

You choose all targets for the spell after revealing cards you want to splice, including any targets required by the text of any of those cards. You may choose a different target for each instance of the word “target” on the resulting spell.

Through the Breach — ruling 5

Putting the card onto the battlefield is optional. When the ability resolves, you can choose not to.

Through the Breach : règles, fonctionnement et interactions (MTG)

Through the Breach 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

You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice that creature at the beginning of the next end step. Splice onto Arcane (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

How it works : Through the Breach

Original English text — Wizards of the Coast / Scryfall

#1June 7, 2013· Wizards of the Coast
If all of the spell’s targets are illegal when the spell tries to resolve, it won’t resolve and none of its effects will happen.
No other card is named in this ruling.
#2June 7, 2013· Wizards of the Coast
You reveal all cards you intend to splice at the same time. Each individual card can be spliced only once onto any one spell.
No other card is named in this ruling.
#3June 7, 2013· Wizards of the Coast
A card with a splice ability can’t be spliced onto itself because the spell is on the stack (and not in your hand) when you reveal the cards you want to splice onto it.
No other card is named in this ruling.
#4June 7, 2013· Wizards of the Coast
You choose all targets for the spell after revealing cards you want to splice, including any targets required by the text of any of those cards. You may choose a different target for each instance of the word “target” on the resulting spell.
No other card is named in this ruling.
#5May 1, 2007· Wizards of the Coast
Putting the card onto the battlefield is optional. When the ability resolves, you can choose not to.
No other card is named in this ruling.