When Raganorn unsealed the catacombs, he found more than the dead and their treasures.

Murk Dwellers

Whenever this creature attacks and isn't blocked, it gets +2/+0 until end of combat.

Fifth Edition

If Murk Dwellers attacks and is not blocked, it gets +2/+0 until end of turn.

Introductory Two-Player Set

Rivals Quick Start Set

Renaissance

Fourth Edition

When attacking and not blocked, Murk Dwellers gets +2/+0 until end of turn.

An 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.