Tiamat's Bane

This magical shortsword deals 1d6 slashing damage, has the "finesse" property, and adds
+1 to attack and damage rolls. It deals an additional 1d6 slashing damage against dragons.
Requires attunement. You can speak the command word "Lightning", causing it to deal an additional 2d6 lightning damage on its next hit. This property can't be used again until the next dawn.