Giant Slayer
Weapon (Any Simple or Martial), rare · 2024 rules, SRD 5.2
You gain a +1 bonus to attack rolls and damage rolls made with this magic weapon. When you hit a Giant with this weapon, the Giant takes an extra 2d6 damage of the weapon's type and must succeed on a DC 15 Strength saving throw or have the Prone condition.
Also in the 2014 rules (SRD 5.1).