Whisperwood Elemental — ruling 1

The last ability grants that ability to face-up nontoken creatures you control as that ability resolves. Creatures that come under your control later in the turn won't have that ability.

Whisperwood Elemental — ruling 2

The face-down permanent is a 2/2 creature with no name, mana cost, creature types, or abilities. It's colorless and has a mana value of 0. Other effects that apply to the permanent can still grant or change any of these characteristics.

Whisperwood Elemental — ruling 3

Any time you have priority, you may turn a manifested creature face up by revealing that it's a creature card (ignoring any copy effects or type-changing effects that might be applying to it) and paying its mana cost. This is a special action. It doesn't use the stack and can't be responded to.

Whisperwood Elemental — ruling 4

If a manifested creature would have morph if it were face up, you may also turn it face up by paying its morph cost.

Whisperwood Elemental — ruling 5

Unlike a face-down creature that was cast using the morph ability, a manifested creature may still be turned face up after it loses its abilities if it's a creature card.

Whisperwood Elemental — ruling 6

Because the permanent is on the battlefield both before and after it's turned face up, turning a permanent face up doesn't cause any enters-the-battlefield abilities to trigger.

Whisperwood Elemental — ruling 7

Because face-down creatures don't have names, they can't have the same name as any other creature, even another face-down creature.

Whisperwood Elemental — ruling 8

A permanent that turns face up or face down changes characteristics but is otherwise the same permanent. Spells and abilities that were targeting that permanent, as well as Auras and Equipment that were attached to the permanent, aren't affected.

Whisperwood Elemental : règles, fonctionnement et interactions (MTG)

Whisperwood Elemental 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

At the beginning of your end step, manifest the top card of your library. (Put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.) Sacrifice this creature: Until end of turn, face-up nontoken creatures you control gain "When this creature dies, manifest the top card of your library."

How it works : Whisperwood Elemental

Original English text — Wizards of the Coast / Scryfall

#1November 24, 2014· Wizards of the Coast
The last ability grants that ability to face-up nontoken creatures you control as that ability resolves. Creatures that come under your control later in the turn won't have that ability.
No other card is named in this ruling.
#2November 24, 2014· Wizards of the Coast
The face-down permanent is a 2/2 creature with no name, mana cost, creature types, or abilities. It's colorless and has a mana value of 0. Other effects that apply to the permanent can still grant or change any of these characteristics.
No other card is named in this ruling.
#3November 24, 2014· Wizards of the Coast
Any time you have priority, you may turn a manifested creature face up by revealing that it's a creature card (ignoring any copy effects or type-changing effects that might be applying to it) and paying its mana cost. This is a special action. It doesn't use the stack and can't be responded to.
Card named in this ruling
Manifest
#4November 24, 2014· Wizards of the Coast
If a manifested creature would have morph if it were face up, you may also turn it face up by paying its morph cost.
Card named in this ruling
Manifest
#5November 24, 2014· Wizards of the Coast
Unlike a face-down creature that was cast using the morph ability, a manifested creature may still be turned face up after it loses its abilities if it's a creature card.
Card named in this ruling
Manifest
#6November 24, 2014· Wizards of the Coast
Because the permanent is on the battlefield both before and after it's turned face up, turning a permanent face up doesn't cause any enters-the-battlefield abilities to trigger.
No other card is named in this ruling.
#7November 24, 2014· Wizards of the Coast
Because face-down creatures don't have names, they can't have the same name as any other creature, even another face-down creature.
No other card is named in this ruling.
#8November 24, 2014· Wizards of the Coast
A permanent that turns face up or face down changes characteristics but is otherwise the same permanent. Spells and abilities that were targeting that permanent, as well as Auras and Equipment that were attached to the permanent, aren't affected.
No other card is named in this ruling.
#9November 24, 2014· Wizards of the Coast
Turning a permanent face up or face down doesn't change whether that permanent is tapped or untapped.
No other card is named in this ruling.
#10November 24, 2014· Wizards of the Coast
At any time, you can look at a face-down permanent you control. You can't look at face-down permanents you don't control unless an effect allows you to or instructs you to.
No other card is named in this ruling.
#11November 24, 2014· Wizards of the Coast
If a face-down permanent you control leaves the battlefield, you must reveal it. You must also reveal all face-down spells and permanents you control if you leave the game or if the game ends.
No other card is named in this ruling.
#12November 24, 2014· Wizards of the Coast
You must ensure that your face-down spells and permanents can easily be differentiated from each other. You're not allowed to mix up the cards that represent them on the battlefield in order to confuse other players. The order they entered the battlefield should remain clear. Common methods for indicating this include using markers or dice, or simply placing them in order on the battlefield. You must also track how each became face down (manifested, cast face down using the morph ability, and so on).
Card named in this ruling
Manifest
#13November 24, 2014· Wizards of the Coast
There are no cards in the Fate Reforged set that would turn a face-down instant or sorcery card on the battlefield face up, but some older cards can try to do this. If something tries to turn a face-down instant or sorcery card on the battlefield face up, reveal that card to show all players it's an instant or sorcery card. The permanent remains on the battlefield face down. Abilities that trigger when a permanent turns face up won't trigger, because even though you revealed the card, it never turned face up.
No other card is named in this ruling.
#14November 24, 2014· Wizards of the Coast
If a double-faced card is manifested, it will be put onto the battlefield face down. While face down, it can't transform. If the front face of the card is a creature card, you can turn it face up by paying its mana cost. If you do, its front face will be up.
Card named in this ruling
Manifest