Isareth the Awakener — ruling 1

Isareth's triggered ability goes on the stack without a target. While that ability is resolving, you may pay {X}. When you do, a second ability triggers and you pick a target creature card to return. This is different from abilities that say "If you do . . ." in that players may cast spells and activate abilities after mana is paid and the target creature card is chosen, but before that card is returned.

Isareth the Awakener — ruling 2

Because all attacking creatures are chosen at once, a creature returned this way can't attack during the same combat as it returns, even if it has haste.

Isareth the Awakener — ruling 3

If a card in your graveyard has {X} in its mana cost, X is considered to be 0.

Isareth the Awakener — ruling 4

If you somehow remove a corpse counter from a creature Isareth has returned to the battlefield, the replacement effect that will exile it continues to apply. The counter is only to help remind you which creatures will be exiled if they would leave the battlefield.

Isareth the Awakener — ruling 5

If Isareth leaves the battlefield, the replacement effect continues to apply. If one of the creatures it returned would leave the battlefield, it'll be exiled instead.

Isareth the Awakener — ruling 6

Because to die means to be put into a graveyard from the battlefield, a creature that is exiled instead doesn't "die." Abilities that would trigger when it dies won't trigger.

Isareth the Awakener : règles, fonctionnement et interactions (MTG)

Isareth the Awakener 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

Deathtouch Whenever Isareth attacks, you may pay . When you do, return target creature card with mana value X from your graveyard to the battlefield with a corpse counter on it. If that creature would leave the battlefield, exile it instead of putting it anywhere else.

How it works : Isareth the Awakener

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2018· Wizards of the Coast
Isareth's triggered ability goes on the stack without a target. While that ability is resolving, you may pay . When you do, a second ability triggers and you pick a target creature card to return. This is different from abilities that say "If you do . . ." in that players may cast spells and activate abilities after mana is paid and the target creature card is chosen, but before that card is returned.
No other card is named in this ruling.
#2July 13, 2018· Wizards of the Coast
Because all attacking creatures are chosen at once, a creature returned this way can't attack during the same combat as it returns, even if it has haste.
No other card is named in this ruling.
#3July 13, 2018· Wizards of the Coast
If a card in your graveyard has in its mana cost, X is considered to be 0.
No other card is named in this ruling.
#4July 13, 2018· Wizards of the Coast
If you somehow remove a corpse counter from a creature Isareth has returned to the battlefield, the replacement effect that will exile it continues to apply. The counter is only to help remind you which creatures will be exiled if they would leave the battlefield.
No other card is named in this ruling.
#5July 13, 2018· Wizards of the Coast
If Isareth leaves the battlefield, the replacement effect continues to apply. If one of the creatures it returned would leave the battlefield, it'll be exiled instead.
No other card is named in this ruling.
#6July 13, 2018· Wizards of the Coast
Because to die means to be put into a graveyard from the battlefield, a creature that is exiled instead doesn't "die." Abilities that would trigger when it dies won't trigger.
No other card is named in this ruling.