Daring Discovery — ruling 1

You can cast Daring Discovery with no targets and just discover 4. However, if you choose any targets, and all of those targets are illegal by the time Daring Discovery tries to resolve, it won't resolve and none of its effects will happen. You won't discover 4. As long as one target remains legal, any legal targets won't be able to block this turn, any illegal targets won't be affected, and you'll discover 4.

Daring Discovery — ruling 2

A spell's mana value is determined only by its mana cost. Ignore any alternative costs, additional costs, cost increases, or cost reductions.

Daring Discovery — ruling 3

When you discover, you must exile cards. The only optional part of the ability is whether you cast the exiled card or put it into your hand.

Daring Discovery — ruling 4

You exile the cards face up. All players will be able to see them.

Daring Discovery — ruling 5

If you cast a spell "without paying its mana cost", you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the spell has any mandatory additional costs, you must pay those to cast it.

Daring Discovery — ruling 6

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

Daring Discovery — ruling 7

If you can't cast the discovered card (perhaps because there are no legal targets for the spell), you'll put it into your hand.

Daring Discovery — ruling 8

Some spells and abilities that cause you to discover may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won't resolve and you won't discover.

Daring Discovery : règles, fonctionnement et interactions (MTG)

Daring Discovery 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

Up to three target creatures can't block this turn. Discover 4. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

How it works : Daring Discovery

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
You can cast Daring Discovery with no targets and just discover 4. However, if you choose any targets, and all of those targets are illegal by the time Daring Discovery tries to resolve, it won't resolve and none of its effects will happen. You won't discover 4. As long as one target remains legal, any legal targets won't be able to block this turn, any illegal targets won't be affected, and you'll discover 4.
No other card is named in this ruling.
#2November 10, 2023· Wizards of the Coast
A spell's mana value is determined only by its mana cost. Ignore any alternative costs, additional costs, cost increases, or cost reductions.
No other card is named in this ruling.
#3November 10, 2023· Wizards of the Coast
When you discover, you must exile cards. The only optional part of the ability is whether you cast the exiled card or put it into your hand.
No other card is named in this ruling.
#4November 10, 2023· Wizards of the Coast
You exile the cards face up. All players will be able to see them.
No other card is named in this ruling.
#5November 10, 2023· Wizards of the Coast
If you cast a spell "without paying its mana cost", you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the spell has any mandatory additional costs, you must pay those to cast it.
No other card is named in this ruling.
#6November 10, 2023· Wizards of the Coast
If the discovered 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.
#7November 10, 2023· Wizards of the Coast
If you can't cast the discovered card (perhaps because there are no legal targets for the spell), you'll put it into your hand.
No other card is named in this ruling.
#8November 10, 2023· Wizards of the Coast
Some spells and abilities that cause you to discover may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won't resolve and you won't discover.
No other card is named in this ruling.
#9November 10, 2023· Wizards of the Coast
The mana value of a split card is determined by the combined mana cost of its two halves. If discover allows you to cast a split card, you may cast either half (as long as its mana value is less than or equal to the effect's discover value) but not both halves.
No other card is named in this ruling.
#10November 10, 2023· Wizards of the Coast
If you discover an adventurer card, split card, or modal double-faced card, you might be able to cast that card with either set of characteristics depending on the effect's discover value. For example, if you discover 4 and reveal Galvanic Giant (an adventurer card from Wilds of Eldraine with a mana value of 4), you could cast Galvanic Giant, but not Storm Reading (its Adventure, which has a mana value of 7). If you discover 7 and reveal Galvanic Giant, you could cast either Galvanic Giant or Storm Reading.
No other card is named in this ruling.