One and four. Mysterious setting and the analysis of the evilness of human nature
This is irony.
It is irony because war is anything but kind. Alliteration would be if both words started with the same letter. Style is not a device, and a simile is when you compare something to something.
I sentence that contains an element of bias could be one that states an opinion. For example, "I think her shoes are ugly, mine are better." the person talking is biased because they really like their shoes.