Charlie the Unicorn was done in Flash, that is at least the initial episode.

All of Stone Trek (a superb Star Trek TOS/Flintstones crossover parody – https://www.angelfire.com/fl/sapringer/STDOTCOM.html) was done in Flash.

All the work of Y0UNG-HAE CHANG HEAVY INDUSTRIES up until 2018 or so was in Flash (last version of their page before they switched to video files: https://web.archive.org/web/20180109044355/https://www.yhcha...).