Nascent Metamorph — ruling 1

The creature card that Nascent Metamorph becomes a copy of is put onto the bottom of the library along with any other cards.

Nascent Metamorph — ruling 2

If the target opponent has no creature cards in their library, Nascent Metamorph doesn't become a copy of anything. The cards are returned to that library in a random order.

Nascent Metamorph — ruling 3

If another permanent becomes a copy of Nascent Metamorph, it will become whatever Nascent Metamorph is copying. It remains a copy when Nascent Metamorph's effect ends.

Nascent Metamorph — ruling 4

If an effect begins to apply to Nascent Metamorph before it becomes a copy, that effect will continue to apply.

Nascent Metamorph — ruling 5

If Nascent Metamorph becomes a copy of a legendary card with the same name as a legendary permanent you control, you'll put one of them into its owner's graveyard.

Nascent Metamorph — ruling 6

If Nascent Metamorph becomes a copy of an object with a set of linked abilities (for example, one ability that exiles a card and another that refers to the card "exiled with" the object), that link only lasts as long as Nascent Metamorph is copying that object. If it stops being a copy of that object and then becomes a copy again later, the link is lost.

Nascent Metamorph : règles, fonctionnement et interactions (MTG)

Nascent Metamorph 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

Whenever this creature attacks or blocks, target opponent reveals cards from the top of their library until they reveal a creature card. This creature becomes a copy of that card until end of turn. Then that player puts all cards revealed this way on the bottom of their library in a random order.

How it works : Nascent Metamorph

Original English text — Wizards of the Coast / Scryfall

#1April 17, 2020· Wizards of the Coast
The creature card that Nascent Metamorph becomes a copy of is put onto the bottom of the library along with any other cards.
No other card is named in this ruling.
#2April 17, 2020· Wizards of the Coast
If the target opponent has no creature cards in their library, Nascent Metamorph doesn't become a copy of anything. The cards are returned to that library in a random order.
No other card is named in this ruling.
#3April 17, 2020· Wizards of the Coast
If another permanent becomes a copy of Nascent Metamorph, it will become whatever Nascent Metamorph is copying. It remains a copy when Nascent Metamorph's effect ends.
No other card is named in this ruling.
#4April 17, 2020· Wizards of the Coast
If an effect begins to apply to Nascent Metamorph before it becomes a copy, that effect will continue to apply.
No other card is named in this ruling.
#5April 17, 2020· Wizards of the Coast
If Nascent Metamorph becomes a copy of a legendary card with the same name as a legendary permanent you control, you'll put one of them into its owner's graveyard.
No other card is named in this ruling.
#6April 17, 2020· Wizards of the Coast
If Nascent Metamorph becomes a copy of an object with a set of linked abilities (for example, one ability that exiles a card and another that refers to the card "exiled with" the object), that link only lasts as long as Nascent Metamorph is copying that object. If it stops being a copy of that object and then becomes a copy again later, the link is lost.
No other card is named in this ruling.