Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Assassin's Blade 
Instant · Uncommon · Portal · #80
Cast this spell only during the declare attackers step and only if you've been attacked this step.
Destroy target nonblack attacking creature.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper