Cheapest priced copy (Fate Reforged): $0.35 at Card Kingdom, near mint, their price list as of .
Will of the Naga 
Instant · Common · Fate Reforged · #58
Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fate Reforged | 58 | Common | $0.35 | $0.49 |
6 rulings from Wizards of the Coast
- 24 November 2014Will of the Naga tracks the creatures, but not their controllers. If any of those creatures changes controllers before its first controller's next untap step, then it won't untap during its new controller's next untap step.
- 24 November 2014Will of the Naga can target creatures that are already tapped. Those creatures won't untap during their controller's next untap step.
- 24 November 2014If you chose two targets and one is an illegal target as Will of the Naga resolves, that creature won't become tapped and it won't be stopped from untapping during its controller's next untap step. It won't be affected by Will of the Naga in any way.
- 19 March 2021Because 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.
- 19 March 2021You 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.
- 19 March 2021Delve 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.