User blog comment:Zadymek/Boss vs boss/@comment-4796846-20180606181032

This is incorrect, and I have experienced both of these situations as I ran through BBI again recently (PS3 version). Death immediatly spawned upon entering The Forgotten Hall the first time, while the Lich was still there; and I've had an Elder Ogre spawn in the Bloodless Stockade's sewers while Death was roaming; not once, but TWICE (the first time, Death somehow got stuck in the smaller room where Leapworms spawn by the dozens on the floor and I managed to deal with the Elder Ogre on its own).
 * 1) "The Death/Garm would never appear if there's a Lich prowling around The Forgotten Hall."
 * 2) "Elder ogre will not show up untill one banishes Death from Bloodless Stockade."

This is further proven false because we know that Death and Cursed Dragons can both spawn in rooms with Condemned Gorecyclops (that is how we know that not only Death can be aggroed by the Gorecyclops and attack him, but it also does insta-kill him, although this gives you no experience or loot). I've had Death spawn with a C. Gorecyclops only once, but it does happen.

However, the rest of your post is correct, as far as I can tell; it's possible to pit room bosses against necrophages, but getting them to spawn with even a sliver of consistence is tricky. The "cooldown" glitch seems to be a result of conflict between the zoning mechanic and how necrophagous enemies spawn, since they do have a natural timer during which no more enemies will appear in that room after they've been killed, even with Rancid Bait Meat (this is clear in the Duskmoon Tower, since it's the best place to farm Cursed Dragons; when they are brought in via bait, you can zone and kill up to four dragons if you're fast enough, but once a certain amount of time passes after you've deployed the bait, the area enters in cooldown regardless of how many dragons you killed, or how much you zone in and out. However, warping back to the isle's entrance seems to reset this cooldown). This is why you "lose" the necrophagous enemies if you zone out, back in, and then leave again. Perhaps a small unintended behaviour on the code, perhaps a safety measure to ensure the mechanic doesn't glitch too hard.