Cheapest priced copy (Dominaria United): $0.49 at Card Kingdom, near mint, their price list as of .
Ivy, Gleeful Spellthief 
Legendary Creature — Faerie Rogue · 2/1 · Rare · Dominaria United · #300
Flying
Whenever a player casts a spell that targets only a single creature other than Ivy, you may copy that spell. The copy targets Ivy. (A copy of an Aura spell becomes a token.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 201 | Rare | $0.49 | $0.79 |
| Dominaria United | 300 | Rare | $0.49 | $0.79 |
| Dominaria United | 341 | Rare | — | $0.99 |
| Dominaria United Promos | 201p | Rare | $2.49 | $3.49 |
| Dominaria United Promos | 201s | Rare | — | $2.99 |
8 rulings from Wizards of the Coast
- 9 September 2022If the spell that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. You can't choose a different one.
- 9 September 2022The second ability triggers whenever a player casts a spell that targets only one creature and no other object or player. It doesn't matter who controls the creature.
- 9 September 2022The copy is created even if the spell that caused the ability to trigger has been countered by the time the ability resolves. The copy resolves before the original spell.
- 9 September 2022The controller of a copy can't choose to pay any additional costs for the copy. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too. Notably, if the spell you copy was kicked, the copies will also be kicked.
- 9 September 2022The copy that Ivy, Gleeful Spellthief's second ability creates is created on the stack, so it's not "cast." Other abilities that trigger when a player casts a spell won't trigger.
- 9 September 2022If the spell that's copied has an X whose value was determined as it was cast, the copy has the same value of X.
- 9 September 2022If a spell has multiple targets but all of them are the same creature, Ivy, Gleeful Spellthief's second ability will trigger.
- 9 September 2022If Ivy, Gleeful Spellthief isn't a legal target for the spell, no copy can be created.