Cheapest priced copy (Portal Second Age): $0.69 at Card Kingdom, near mint, their price list as of .
Abyssal Nightstalker 
Creature — Nightstalker · 2/2 · Uncommon · Portal Second Age · #61
Whenever this creature attacks and isn't blocked, defending player discards a card.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.69 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Portal Second Age | 61 | Uncommon | $0.69 | — |
One ruling from Wizards of the Coast
- 15 April 2013An ability that triggers when something "attacks and isn't blocked" triggers in the declare blockers step after blockers are declared if (1) that creature is attacking and (2) no creatures are declared to block it. It will trigger even if that creature was put onto the battlefield attacking rather than having been declared as an attacker in the declare attackers step.