Tombstalker
Creature — Demon
Flying
Delve (Each card you exile from your graveyard while casting this spell pays for 
.)
When it ran out of bodies, it broke down the crypt door and sought new sustenance.
Aleksi Briclot
Time Spiral Remastered (TSR)
• #146Rulings
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.
(wotc • 2021-03-19)
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.
(wotc • 2021-03-19)
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.
(wotc • 2021-03-19)
Rulings
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.
(wotc • 2021-03-19)
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.
(wotc • 2021-03-19)
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.
(wotc • 2021-03-19)