Hazoret's Undying Fury — ruling 1

No lands that you control will untap during your next untap step, even lands that aren't tapped as this spell resolves. This includes lands that enter the battlefield after this spell resolves.

Hazoret's Undying Fury — ruling 2

Each individual spell you cast this way must have mana value 5 or less. Their total mana value could be greater.

Hazoret's Undying Fury — ruling 3

No player may take any actions between the time you shuffle your library and the time you exile the top four cards.

Hazoret's Undying Fury — ruling 4

If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs, such as emerge costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, you must pay those to cast the card.

Hazoret's Undying Fury — ruling 5

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Hazoret's Undying Fury — ruling 6

If any abilities trigger as you cast any of those cards, they won't be put on the stack until after you're done casting them. They'll resolve before any of those spells.

Hazoret's Undying Fury — ruling 7

If you cast any of those cards, you do so as part of the resolution of Hazoret's Undying Fury. You can't wait to cast them later in the turn.

Hazoret's Undying Fury — ruling 8

If a spell you cast this way targets another spell, it may target a spell you cast earlier during the resolution of Hazoret's Undying Fury. It may target Hazoret's Undying Fury as well, but Hazoret's Undying Fury will be put into your graveyard soon afterwards and the spell's target will become illegal.

Hazoret's Undying Fury : règles, fonctionnement et interactions (MTG)

Hazoret's Undying Fury 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

Shuffle your library, then exile the top four cards. You may cast any number of spells with mana value 5 or less from among them without paying their mana costs. Lands you control don't untap during your next untap step.

How it works : Hazoret's Undying Fury

Original English text — Wizards of the Coast / Scryfall

#1July 14, 2017· Wizards of the Coast
No lands that you control will untap during your next untap step, even lands that aren't tapped as this spell resolves. This includes lands that enter the battlefield after this spell resolves.
No other card is named in this ruling.
#2July 14, 2017· Wizards of the Coast
Each individual spell you cast this way must have mana value 5 or less. Their total mana value could be greater.
No other card is named in this ruling.
#3July 14, 2017· Wizards of the Coast
No player may take any actions between the time you shuffle your library and the time you exile the top four cards.
No other card is named in this ruling.
#4July 14, 2017· Wizards of the Coast
If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs, such as emerge costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, you must pay those to cast the card.
No other card is named in this ruling.
#5July 14, 2017· Wizards of the Coast
If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
No other card is named in this ruling.
#6July 14, 2017· Wizards of the Coast
If any abilities trigger as you cast any of those cards, they won't be put on the stack until after you're done casting them. They'll resolve before any of those spells.
No other card is named in this ruling.
#7July 14, 2017· Wizards of the Coast
If you cast any of those cards, you do so as part of the resolution of Hazoret's Undying Fury. You can't wait to cast them later in the turn.
No other card is named in this ruling.
#8July 14, 2017· Wizards of the Coast
If a spell you cast this way targets another spell, it may target a spell you cast earlier during the resolution of Hazoret's Undying Fury. It may target Hazoret's Undying Fury as well, but Hazoret's Undying Fury will be put into your graveyard soon afterwards and the spell's target will become illegal.
No other card is named in this ruling.
#9July 14, 2017· Wizards of the Coast
If more than one spell says that lands you control don't untap during your next untap step, the effects will all wear off during that untap step. You'll untap lands you control during your untap step after that one.
No other card is named in this ruling.