This is a little user script for Tampermonkey who aim to resolve a simple issue with Youtube:
The lack of fine tuning about which videos you want to delete from your playlists. Youtube recently added a button "Delete watched videos" for the watch later playlist. But this button will delete EVERY started watched videos. Even the ones you didn't finished to watch yet.
This script solve the issue by adding a button on Youtube to remove watched videos with more than X percent from any playlist.
It also add a shortcut for each video in the list to quickly remove each video without the need to go into the sub-menu.
You need to have ViolentMonkey or TamperMonkey extension installed in your browser. Then simply click to this install link and add this userscript to your extensions.
You can also go to the GreasyFork page and install it from there.