I'm sure I'm not the only one who's thought of this, but shortly after discovering FurDoom, the first thing I immediately did was combine it with HDoom, to some rather "interesting" results! ;) (I posted screenshots in this tweet) 

NGL it's funny how I can horny-bonk the HDoom demon girls with FurDoom's bonk bat now. XD 

BTW before anyone asks, unfortunately merging FurDoom with HDoom will not allow you to fuck the thicc furry demons... However, you can summon the HDoom demons and fuck 'em while the thicc furries watch! ( ͡° ͜ʖ ͡°) 

If you wanna give this little experiment a try, you can download the latest version of HDoom on HDoomGuy's Newgrounds page.