Summon Undead — ruling 1

If you have fewer than three cards in your library, you can't choose to mill any cards this way.

Summon Undead — ruling 2

You return a creature card if there is one to return, even if you chose not to mill three cards.

Summon Undead — ruling 3

You can return a creature card that you milled or one that was already in your graveyard.

Summon Undead : règles, fonctionnement et interactions (MTG)

Summon Undead 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

You may mill three cards. Then return a creature card from your graveyard to the battlefield. (To mill a card, put the top card of your library into your graveyard.)

How it works : Summon Undead

Original English text — Wizards of the Coast / Scryfall

#1June 10, 2022· Wizards of the Coast
If you have fewer than three cards in your library, you can't choose to mill any cards this way.
No other card is named in this ruling.
#2June 10, 2022· Wizards of the Coast
You return a creature card if there is one to return, even if you chose not to mill three cards.
No other card is named in this ruling.
#3June 10, 2022· Wizards of the Coast
You can return a creature card that you milled or one that was already in your graveyard.
No other card is named in this ruling.