The source code of Reliquary port for Minecraft Bedrock! Reliquary was originally made by x3n0ph0b3 and TheMike, and is now maintained by P3pp3rF1y. Port made by Brunum.
It's GPLv3 (with one of the sounds under CC Attribution License).
Basically, do whatever you want, as long as it's free, open source, and stays under GPL. (Yes, that allows you to use it in your addonpack.)