Javelin of Lightning
Weapon (javelin), uncommon · 2014 rules, SRD 5.1
When thrown, speak the command word to turn it into a 5-ft wide lightning bolt line to the target: 4d6 lightning (DC 13 Dex half), target takes the javelin damage + 4d6. Once per dawn.
Also in the 2024 rules (SRD 5.2).