Niv-Mizzet Reborn — ruling 1

A "color pair" is exactly two colors. There are ten color pairs in Magic: white-blue, white-black, blue-black, blue-red, black-red, black-green, red-green, red-white, green-white, and green-blue.

Niv-Mizzet Reborn — ruling 2

If the top ten cards of your library don't contain all ten color pairs, you choose as many cards as you can and put those cards into your hand.

Niv-Mizzet Reborn : règles, fonctionnement et interactions (MTG)

Niv-Mizzet Reborn 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

Flying When Niv-Mizzet enters, reveal the top ten cards of your library. For each color pair, choose a card that's exactly those colors from among them. Put the chosen cards into your hand and the rest on the bottom of your library in a random order.

How it works : Niv-Mizzet Reborn

Original English text — Wizards of the Coast / Scryfall

#1May 3, 2019· Wizards of the Coast
A "color pair" is exactly two colors. There are ten color pairs in Magic: white-blue, white-black, blue-black, blue-red, black-red, black-green, red-green, red-white, green-white, and green-blue.
No other card is named in this ruling.
#2May 3, 2019· Wizards of the Coast
If the top ten cards of your library don't contain all ten color pairs, you choose as many cards as you can and put those cards into your hand.
No other card is named in this ruling.