Dreamstealer — ruling 1

For each card with eternalize, a corresponding game play supplement token can be found in some Hour of Devastation booster packs. These supplements are not required to play with cards with eternalize; you can use the same items to represent an eternalized token as you would any other token.

Dreamstealer — ruling 2

If a creature card with eternalize is put into your graveyard during your main phase, you'll have priority immediately afterward. You can activate its eternalize ability before any player can try to exile it, such as with Crook of Condemnation, if it's legal for you to do so.

Dreamstealer — ruling 3

Once you've activated an eternalize ability, the card is immediately exiled. Opponents can't try to stop the ability by exiling the card with an effect such as that of Crook of Condemnation.

Dreamstealer — ruling 4

The token copies exactly what was printed on the original card and nothing else, except the characteristics specifically modified by eternalize. It doesn't copy any information about the object the card was before it was put into your graveyard.

Dreamstealer — ruling 5

The token is a Zombie in addition to its other types and is black instead of its other colors. Its base power and toughness are 4/4. It has no mana cost, and thus its mana value is 0. These are copiable values of the token that other effects may copy.

Dreamstealer — ruling 6

If the card copied by the token had any "when [this permanent] enters the battlefield" abilities, then the token also has those abilities and will trigger them when it's created. Similarly, any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities that the token has copied will also work.

Dreamstealer : règles, fonctionnement et interactions (MTG)

Dreamstealer 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

Menace Whenever this creature deals combat damage to a player, that player discards that many cards. Eternalize (, Exile this card from your graveyard: Create a token that's a copy of it, except it's a 4/4 black Zombie Human Wizard with no mana cost. Eternalize only as a sorcery.)

How it works : Dreamstealer

Original English text — Wizards of the Coast / Scryfall

#1July 14, 2017· Wizards of the Coast
For each card with eternalize, a corresponding game play supplement token can be found in some Hour of Devastation booster packs. These supplements are not required to play with cards with eternalize; you can use the same items to represent an eternalized token as you would any other token.
No other card is named in this ruling.
#2July 14, 2017· Wizards of the Coast
If a creature card with eternalize is put into your graveyard during your main phase, you'll have priority immediately afterward. You can activate its eternalize ability before any player can try to exile it, such as with Crook of Condemnation, if it's legal for you to do so.
No other card is named in this ruling.
#3July 14, 2017· Wizards of the Coast
Once you've activated an eternalize ability, the card is immediately exiled. Opponents can't try to stop the ability by exiling the card with an effect such as that of Crook of Condemnation.
No other card is named in this ruling.
#4July 14, 2017· Wizards of the Coast
The token copies exactly what was printed on the original card and nothing else, except the characteristics specifically modified by eternalize. It doesn't copy any information about the object the card was before it was put into your graveyard.
No other card is named in this ruling.
#5July 14, 2017· Wizards of the Coast
The token is a Zombie in addition to its other types and is black instead of its other colors. Its base power and toughness are 4/4. It has no mana cost, and thus its mana value is 0. These are copiable values of the token that other effects may copy.
No other card is named in this ruling.
#6July 14, 2017· Wizards of the Coast
If the card copied by the token had any "when [this permanent] enters the battlefield" abilities, then the token also has those abilities and will trigger them when it's created. Similarly, any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities that the token has copied will also work.
No other card is named in this ruling.