Update 0.7.7.0 can be downloaded here: ReignofTerror_0.7.7.0.7z - Google Drive
Changelog is inside the download file.
Requires 0.7.6.0 or higher. Download and extract the zipfile into your …/Grim Dawn/mods folder and click Yes to All when asked to overwrite files.
Edit: There’s an unclear line in the changelog:
All Diablo 2 Unique and Set items, increased flat damage by 15%
This damage increase applies only to two-handed melee weapons.