As I started developing the concept of Dragon's Delve, I knew I had to serve the classic archetypes of the 1st level dungeon with a hefty dose of humanoids for the PCs to fight. But what would it be? Kobolds? Goblins? Orcs? They all had their advantages and disadvantages. They all ran the risk of being overused, but I didn't want to create something new for this (there will be lots of new monsters later). Like I said, I wanted to go the more classic route.
So then it occurred to me--what if I used them all? What if some unifying force had gathered them together, despite different approaches, alignments, and outlooks?
The purpose of the Bestial Host is for you, the DM, to provide an ongoing menace for the PCs--an intelligent but rather straightforward threat that has the potential to grow in power as the player characters do.
Having all the humanoids together presents you with the opportunity to individualize the combatants. You can play up the archetypes, and play them off of each other. The goblins can be devious little buggers, the orcs savage and bestial, the hobgoblins cruel and domineering, and the kobolds can be comedy relief (if you want--they could also be tricksy and nasty). And of course, there's the degenerate humans, which are basically bloodthirsty cavemen thrown in for good measure. As they charge into battle with the PCs, shouting oaths to the Beast God, the hobgoblins can boss around the others, the goblins can work together to aid their larger brethren, and the orcs can ignore the rest and just wade into the fight. Each type of humanoid has its own personality and tactics that you can utilize without feeling trite or repetitious, because each type of humanoid is just one of many, rather than the only one on stage.
There will be encounters with the Bestial Host later on as well, both deeper in the dungeon and in bonus encounters involving them elsewhere. Eventually, we'll see the stats for Scrall, their leader, and more (like the barghests secretly infiltrating their ranks posing as goblins for their own nefarious reasons). While not a constant threat, they'll be an ongoing presence in the campaign at large.
If you're a fan of miniatures, here are some cool ones that you could use for the Bestial Host:
Art by Eric Lofgren