Cheapest priced copy (Mirage): $0.69 at Card Kingdom, near mint, their price list as of .
Acidic Dagger 
Artifact · Rare · Mirage · #291
{4}, {T}: Whenever target creature deals combat damage to a non-Wall creature this turn, destroy that non-Wall creature. When the targeted creature leaves the battlefield this turn, sacrifice this artifact. Activate only before blockers are declared.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.69 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirage | 291 | Rare | $0.69 | — |
2 rulings from Wizards of the Coast
- 4 October 2004Acidic Dagger does not affect the creature if all damage is prevented or redirected.
- 20 September 2013If a turn has multiple combat phases, the ability can only be activated before the beginning of the Declare Blockers Step of the first combat phase in that turn.