Elvish Vatkeeper

To incubate N, create an Incubator token that enters the battlefield with N +1/+1 counters on it. See rule 111.10i.

An Incubator token is a transforming double-faced token. Its front face is a colorless Incubator artifact with “{2}: Transform this artifact.” Its back face is a 0/0 colorless Phyrexian artifact creature named “Phyrexian Token.”

To transform a permanent, turn it over so that its other face is up. Only transforming tokens and permanents represented by transforming double-faced cards can transform. (See rule 712, “Double-Faced Cards.”)

Although transforming a permanent uses the same physical action as turning a permanent face up or face down, they are different game actions. Abilities that trigger when a permanent is turned face down won’t trigger when that permanent transforms, and so on.

If a spell or ability instructs a player to transform a permanent that isn’t represented by a transforming token or a transforming double-faced card, nothing happens.

If a spell or ability instructs a player to transform a permanent, and the face that permanent would transform into is represented by an instant or sorcery card face, or is a transforming token that was created with an instant or sorcery face, nothing happens.

Some triggered abilities trigger when an object “transforms into” an object with a specified characteristic. Such an ability triggers if the object either transforms or converts (see rule 701.50) and has the specified characteristic immediately after it does so.

If an activated or triggered ability of a permanent that isn’t a delayed triggered ability of that permanent tries to transform it, the permanent does so only if it hasn’t transformed or converted since the ability was put onto the stack. If a delayed triggered ability of a permanent tries to transform that permanent, the permanent does so only if it hasn’t transformed or converted since that delayed triggered ability was created. In both cases, if the permanent has already transformed or converted, an instruction to do either is ignored.

Some spells and abilities refer to a “transformed permanent.” This phrase refers to a permanent on the battlefield with its back face up that’s also a transforming double-faced card or a transforming token. A permanent with its front face up is never considered a transformed permanent, even if it had its back face up previously.

Doubling a creature’s power and/or toughness creates a continuous effect. This effect modifies that creature’s power and/or toughness but doesn’t set those characteristics to a specific value. See rule 613.4c.

To double a creature’s power, that creature gets +X/+0, where X is that creature’s power as the spell or ability that doubles its power resolves. Similarly, an effect that doubles a creature’s toughness gives it +0/+X, where X is that creature’s toughness. Doubling a creature’s power and toughness gives it +X/+Y, where X is its power and Y is its toughness.

If a creature’s power is less than 0 when it’s doubled, doubling that creature’s power instead means that the creature gets -X/-0, where X is the difference between 0 and its power. Similarly, if its toughness is less than 0 when doubled, it gets -0/-X. If one characteristic’s value is negative but the other isn’t when both are doubled, it gets -X/+Y or +X/-Y, as appropriate.

To double a player’s life total, the player gains or loses an amount of life such that their new life total is twice its current value.

To double the number of a kind of counters on a player or permanent, give that player or permanent as many of those counters as that player or permanent already has.

To double the amount of a type of mana in a player’s mana pool, that player adds an amount of mana of that type equal to the amount they already have.

To double an amount of damage a source would deal, that source instead deals twice that much damage. This is a replacement effect.