Empty the Pits — ruling 1

Delve doesn't change a spell's mana cost or mana value. For example, Treasure Cruise's mana value is 8 even if you exiled three cards to cast it.

Empty the Pits — ruling 2

You can exile cards to pay only for generic mana, and you can't exile more cards than the generic mana requirement of a spell with delve. For example, you can't exile more than seven cards from your graveyard to cast Treasure Cruise unless an effect has increased its cost.

Empty the Pits — ruling 3

Because delve isn't an alternative cost, it can be used in conjunction with alternative costs, such as flashback. It can also be used to pay for additional costs that include generic mana.

Empty the Pits : règles, fonctionnement et interactions (MTG)

Empty the Pits 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

Delve (Each card you exile from your graveyard while casting this spell pays for .) Create X tapped 2/2 black Zombie creature tokens.

How it works : Empty the Pits

Original English text — Wizards of the Coast / Scryfall

#1March 19, 2021· Wizards of the Coast
Delve doesn't change a spell's mana cost or mana value. For example, Treasure Cruise's mana value is 8 even if you exiled three cards to cast it.
No other card is named in this ruling.
#2March 19, 2021· Wizards of the Coast
You can exile cards to pay only for generic mana, and you can't exile more cards than the generic mana requirement of a spell with delve. For example, you can't exile more than seven cards from your graveyard to cast Treasure Cruise unless an effect has increased its cost.
No other card is named in this ruling.
#3March 19, 2021· Wizards of the Coast
Because delve isn't an alternative cost, it can be used in conjunction with alternative costs, such as flashback. It can also be used to pay for additional costs that include generic mana.
No other card is named in this ruling.