Difference between Guile Hero and Magnificant Bastard?

I have a character named Luella (hence the name) who's one of the main characters I'm trying to write and I wanted her to be a magnificent bastard, but at the same time, I feel like she would be too overpowered and I tried to make her a guile hero instead, but then I feel like she might not be able to use gambits. But then I questioned about the guile hero and the magnificent bastard archetypes:

-Can a guile hero become a magnificent bastard and/or vice versa? -Are there any similarities between a magnificent bastard and a guile hero? What about differences?

I feel like it would be an interesting character development where a guile hero turns into a magnificent bastard while staying true to her being heroic. What do you guys think?

Hmmm...as much as I hate receiving this advice, I think it is solid all the same. Don't aim for the Magnificent Bastard when trying to write your character. I know that seems counterproductive but hear me out on this one. A Magnificent Bastard is a fairly subjective trope and thus depends on the audience's reactions to a character—in this case Luella's—actions and the results within the story.

However a Guile Hero is something that you can create and pull off relatively well. It is not a subjective state of being and has definite qualities you can give her and set the story around to make them plausible.

For example—one of my stories has a character deceive a group of formerly mutated humans into thinking he could cure them, in order to get them on his side. Some of my readers praised his genius while others denounced him as a Manipulative Bastard who preyed on people's hopes. He was a Guile Hero but the reactions were all over the place.

I hope this helped.

I always figured that the difference between them was in how much direct action the character takes. A Guile Hero works towards a personal goal through direct personal actions that aren't necessarily physical; the Magnificent Bastard does the same but includes others' actions as well to make it an issue of scale.

They're not mutually exclusive, but they require wildly different lengths of story to adequately display. And even then it would be difficult to have them both in the same self-contained single story, without going down the Mary Sue path.

Leaving aside the audience reaction aspect of MB, which Sword of Knowledge nicely summed up, the Guile Hero typically violates fewer rules, and hurts fewer people. They succeed through their brains, and political or manipulative ability, but their methods are typically morally superior to those of an MB.

There are similarities in terms of the fields in which they operate, but where the difference kicks in his the how. To pick an example, in Gundam SEED Lacus Clyne is the resident Guile Hero. She's a politically connected heiress who uses her family money and status, and her own position as a pop singer to rally support against a corrupt regime, creating a network of agents within the ZAFT power structure who eventually defect to her. She's getting people to do what she wants, but is doing it by appealing to their better natures. Conversely, Rau Le Creuset, the resident MB, is trying to steer the war in a worse direction, and is preying on his victims' fears, vulnerabilities, and prejudices to get there. Both are manipulators, both operate in the political field, and both try to utilize the emotions of the people they are talking to, but to very different ends and in very different ways.

Where overlap can kick in is when people start writing antiheroes. Is Batman a Guile Hero or an MB? Good question. Generally I'd say the former, since the people he's going after usually deserve it.

In the end, I'll second what Sword of Knowledge said. Trying to write an MB is a lot like trying to write a Complete Monster. Both are audience reaction tropes, and there's not a lot of point to it. What you're really looking to do, based on your initial post, is write a character who uses their brains to get things done and has a dark streak that becomes more difficult to control. Write that, and let the people who read it afterwards worry about what tropes she fits into.