Cheapest priced copy (Ravnica: Clue Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Code of Constraint 
Instant · Uncommon · The List · #RNA-35
Target creature gets -4/-0 until end of turn.
Draw a card.
Addendum — If you cast this spell during your main phase, tap that creature and it doesn't untap during its controller's next untap step.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ravnica: Clue Edition | 83 | Uncommon | $0.35 | — |
| The List | RNA-35 | Uncommon | $0.35 | — |
| Ravnica Allegiance | 35 | Uncommon | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 25 January 2019If the target creature is an illegal target by the time Code of Constraint tries to resolve, the spell doesn't resolve. You don't draw a card.
- 25 January 2019Code of Constraint can target a creature that's already tapped. If you cast it during your main phase, that creature won't untap during its controller's next untap step.
- 12 January 2024Addendum abilities of instant spells apply while the spell is resolving, not immediately after casting it. If the spell is countered, you don't get the addendum bonus.
- 12 January 2024If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.