Use the asset manager to extract the data (see chapter 1 of PDF).
C:\Program Files (x86)\Steam\steamapps\common\Grim Dawn\resources\creatures\enemies\manticore every place that the hellhound is referenced, you need to reference these files instead. At a minimum, that would be the skill’s DBR file.
copy and paste the files involved into a mod folder
build the mod
launch the custom game.
I got steps 1, 3, 4, 5 done last night in about a half hour, so this isn’t too bad - but the references in step 2 are simply not something I did last night. Please do post about your experiences.