There are often masters who play important roles. For example, Shirou Emiya can be one of the key characters in the Fate - related stories. He has his own goals and ideals which interact with Saber Alter's story.
An alter ego is definitely a fictional character. It can be a way for an author or creator to explore different traits, emotions, or situations that the main character might not be able to express directly. It's a common literary device used to spice up the narrative.
There's also a chance that Dumbledore gets caught by a group of rogue magical creatures. For instance, if he was exploring an area that was supposed to be off - limits to wizards and the creatures there saw him as an intruder. They might not be as rational as wizards and could hold him captive without really understanding who he is.
Well, it could be that Dumbledore has some sort of hidden device or spell that he activates when kidnapped. For example, he could have a charmed object that sends a signal to his allies, like the Order of the Phoenix. His allies then come to his rescue and he manages to escape during the chaos. Also, Dumbledore is extremely intelligent. He might outwit Grindelwald by engaging him in a complex conversation full of riddles and misdirections, which gives him an opportunity to break free.
I'm not sure specifically as it could be a rather niche or new light novel. It might be about a character named Archid who experiences some sort of alteration in the story. Maybe it involves a fantasy world with magic and adventure where Archid's alteration plays a key role in the plot.
Alter Ego Visual Novel is often about exploring different personalities or alter egos within the story. It might involve characters dealing with their inner selves, making choices that reflect different aspects of who they could be, and usually has a strong narrative with various plot twists related to these concepts.
One common theme is redemption. Since Arjuna Alter is a darker version of Arjuna, many fanfics explore his journey towards redemption or at least a better understanding of himself. Another theme is his power and how it's different from the original Arjuna.
One popular alter history novel is 'The Man in the High Castle' by Philip K. Dick. It imagines a world where the Axis powers won World War II. Another is 'Fatherland' by Robert Harris, which is set in a world where Nazi Germany won the war. 'Jonathan Strange & Mr Norrell' by Susanna Clarke also has elements of alter history as it reimagines an England where magic exists in a different way than in our own history.
Well, in the Saber Alter Visual Novel, the story is centered around this unique character. It shows her journey in a world full of challenges. It dives deep into her psyche as an 'alter' form. There are interactions with other characters from the Fate series which shape her story. For example, her relationships with the masters and other servants can be full of tension and cooperation at the same time.