Something I've been thinking about the entire week since finishing Expedition 33 (the video game). I have something of an obsession with the antagonist's motivations. It's what triggers me the most when reading/watching/playing something, and the villain is just evil for no other reason than to be something for the hero to fight against.
To me, the motivations of the antagonist are more important than why the hero steps up to fight against them. After all, in almost every story, it's the big baddy that dictates the actions of the hero and starts the plot to begin with. Just look at how many main characters in this space are just bank self-inserts without any personality and the story works regardless.
For me, a perfect villain is someone who has a clear and understandable motivation for their actions. Someone who follows their own path and isn't just there to push the plot in this or that direction. Someone who is written to act with their own knowledge base in mind and who isn't somehow omniscient. That's what I consider the minimum for a good villain.
A great villain would be someone who I can say is not wrong, just coming to the wrong conclusions or taking the wrong steps to reach their goal. And a perfect villain would be someone who flips me and brings me completely over to their side. I haven't seen any such "perfect villain" in a light novel, but I haven't lost hope yet. The antagonist of Expedition 33 was the example of a perfect villain that made me think about this topic for the last week and Prince Nuada from Hellboy 2 was another one I could come up with.
[META] This was the last Midweek Discussion topic I had prepared. If someone has some more ideas, please send me a DM. Otherwise I might just let them rest and then loop around from the beginning after a while. Or use whatever I can think of at that given day.