Completely unintelligent monsters such as some constructs, some undead, and all vermin, are immune to social manipulation.
Note that some rare monsters do not follow the normal threat mechanics.
Since that time, some of their more minor benefits have been added back in through gear like Ferine Gausape 2, but "intimidation" remains the most important aspect.
Intimidation occurs when a monster of one family is attacking the monster of a family with an inherent advantage over it.
Intimidate does not affect Pokémon with the Full Metal Body Ability.
If the demon you're facing isn't in fire, stick to his face like a bubble-gum sticks under a high schooler's desk.
Now, the strategy will change depending on if the Demon from Below is or not on fire.
An important note is that a good shield for this fight that resists high physical and fire can come in handy blocking their attacks.
There are some applications that have weird little quirks that tend to throw a wrench in things.
NGINX happens to have a very well rounded community that has worked to first address these quirks and then share the resulting configurations.