FOILCheapest priced copy (Jumpstart): $0.79 at Card Kingdom, near mint, their price list as of .
Scholar of the Lost Trove 
Creature — Sphinx · 5/5 · Rare · Jumpstart · #496
Flying
When this creature enters, you may cast target instant, sorcery, or artifact card from your graveyard without paying its mana cost. If an instant or sorcery spell cast this way would be put into your graveyard, exile it instead.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.79 at Card Kingdom
4 rulings from Wizards of the Coast
- 23 June 2020If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 23 June 2020If you wish to cast the target card, you must cast it while the triggered ability is resolving. You can’t cast it later in the turn.
- 23 June 2020If you cast an artifact spell this way, it won’t be exiled if it would be put into your graveyard this turn.
- 23 June 2020If 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 card has any mandatory additional costs, those must be paid to cast the spell.