Yhyjyk

By "ununderstandable" I mean that this character I'm thinking of isn't human. He's more of a devil sort of thing. Of course he still has his motivations, goals, etc, but he's more of a tool rather than a force in the story. He just wants his thing and has basically no emotions or humanity. He doesn't care about the main character or what happens to him, be it good or bad.

He's like the bus in that Sandra Bullock movie hah

Right now I'm in the planning stage. My question is 'Should the conflict include this "tool-character" and be something like "devil against man", or should I consider the conflict to be "the internal struggles of the actual character, which are caused by the tool-character's actions" ?'

Note: I'm fairly new to all this, so I try to grab on to concepts like conflict and theme to better understand how to write

Yes.

In every conflict, you will have the protagonist and the antagonist. Antagonist does not need to be human, or sentient, or even alive in any sense. For example, in Tom Hanks movie Cast Away, the nature itself is such a non-personified antagonist.

But personified antagonist works much better for any story. In your example, "Speed", we have such a person, a villain, no less, so the audience sees the bus as just a tool. If there is anyone human-like to blame in the story, audience will see that one as antagonist. In your story, if this demon-like being is the most personified force opposing your protagonist, he will be seen as antagonist and, consequently, a part of the conflict. If, on the other hand, there is a human villain, while the demon is more like Genie from "Aladdin", then you can focus readers' attention on that human character, while keeping the demon mostly outside of the conflict.

Zelazny wrote a fascinating character who was a demon and a half cast spell. Said character had a need to know what and who he was, where he fit in the scheme of things.

Any sentient being can be understood by the reader. Sometimes the character is one who is so vast and complex, so old and foreign, that he can only be grasped by the other characters but never really understood.

Zelazny’s character was a tool with a purpose and personality.

If it were me, I would write your demon as incidentally in conflict with the MC - giving him about the same consideration as a bug underfoot or some rodent observed. The greater power of the demon will be an advantage, but the MC will have to use wit to prevail despite this strong competition - or fail.

Maybe have it both ways.

Have the protagonist view the tool as the antagonist when it actually isn't. This will waste some of the protagoinst's energy until they figure out who the real antagonist is.

It would be kind of like shouting at the wind for blowing out your candle when there is a panther stalking you.