Cheapest priced copy (Throne of Eldraine): $0.35 at Card Kingdom, near mint, their price list as of .
Once and Future 
Instant · Uncommon · Throne of Eldraine · #168
Return target card from your graveyard to your hand. Put up to one other target card from your graveyard on top of your library. Exile Once and Future.
Adamant — If at least three green mana was spent to cast this spell, instead return those cards to your hand and exile Once and Future.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 168 | Uncommon | $0.35 | $0.49 |
6 rulings from Wizards of the Coast
- 4 October 2019If an effect allows you to cast a spell without paying its mana cost, you can't choose to cast it and pay unless another rule or effect allows you to cast that spell for a cost. Similarly, you can't waive a cost reduction unless that effect says you may.
- 4 October 2019If one of the two target cards is an illegal target by the time Once and Future resolves, you'll put the other in the appropriate zone and exile Once and Future. If both targets are illegal, the spell won't resolve and you won't exile Once and Future.
- 4 October 2019If an instant or sorcery spell has an adamant ability, you perform the spell's instructions in order. You don't perform the adamant instruction before the spell resolves or before any other effects printed above it.
- 4 October 2019You choose which card will be returned to your hand and which will be put on top of your library as you choose those cards as targets, not as Once and Future resolves.
- 4 October 2019If you copy a spell that has an adamant ability, no mana was spent to cast the copy at all, so that ability won't apply.
- 4 October 2019Adamant effects check what mana was actually spent to cast a spell. If an effect allows you to spend mana “as though it were mana” of any color or type, that allows you to spend mana you couldn't otherwise spend, but it doesn't change what mana you spent to cast the spell.