I'm not the most extreme metalhead around, but I know some stuff. So I decided to expand on the suggested Playlist for each great house to help put people in the mood. Each of these playlists include the 3 original songs and then more songs which I felt fit their theme musically and conceptually.
If you want to help collaborate on these playlists in ListenBrainz, let me know!
C.A.R.C.A.S.S.
The original music was all about the speed of the music. Since it allowed for the clean vocals and electronics of BABYMETAL, I took that as allowance to add more clean vocal tracks and futuristic sounds, a lot of which match the theme of the faction. For example Good L_ck (Yo_'re F_cked) from Celldweller is like a perfect theme song for a faction like this.
Goregrinders
Goregrinders were all about that brutal death metal, so I continued the trend with songs tying into the theme conceptually like Doom Slayer by Alex Terrible. And of course this list would never be complete without Face Fisted from Dethklok
Gargamox
I'm not quite sure what theme to go for with Gargamox. Their three songs all seem to be chosen conceptually rather than with a concrete music style. So I tried to stay with songs which invoke the dirty punk aesthetic, and if possible still at extreme metal. I'd probably try to make a pure punk list around them at some point.
Deadsouls
Deadsouls immediately brought me to the bombastic black metal of Cradle of Filth and of course Immortal, but since I am not too much into that scene, I expanded the selection with also some more deeper vocals so long as it matched the theme.
Abhorrers
From the start I had a good idea that the Abhorrers would be all about that Melodeath. While the initial collection was fairly fast paced, I couldn't stop myself throwing a lot of Rotting Christ in there due to how well their concepts fit, and continued from there.
Igorri
I had some trouble decoding what kind of music Igorri would go for. In the end I settled for some technical/prog stuff due to their mad scientist nature, and threw also some songs which just match their theme as a house very well even if technically not as "extreme" as the original 3, like Narcosynthesis from Nevermore and Prime Specimen by Black Comedy.
Remember if you want to help collaborate on these playlists, let me know and I can add you as a collaborator on ListenBrainz!