Xjyuk

Okay, there is some preliminary information for you to be able to answer this question: There is a sword of great power, a McGuffin, and a destined one who wields it. The destined one has two companions. These three we'll call Gang 1, for simplicity.

Then you have the King's Guard, who want to retrieve the sword (it was stolen from the treasury). But also, the leader of the King's Guard wants revenge on one of the members in Gang 1. We'll call these people Gang 2.

Then there is this crime boss, who also wants the sword, for power. Him and his men we'll call Gang 3. He also has a bit of a grudge to someone in Gang 1.

Then we have another crime boss, though he is of a prominent crime family, and he sends his sons on this mission. This is Gang 4, and he is in a feud with Gang 3. Also, one of his sons are one of the destined one's companions. So, his sons want to not only take the sword, for power, but they also want to retrieve the son in Gang 1.

Then you have the destroyer, who has hired a crew, so he can destroy the sword, both due to conviction but also personal motives. He and his crew is Gang 5.

Within Gang 5 is someone who is a bit more educated, and therefore knows the power of the sword, and therefore decides he doesn't want it destroyed, but rather in his hands. So, he stages a mutiny within Gang 5, which will be Gang 6. He also has personal motives involved in this, as he wants to fill his fathers shoes of being a captain (this all happens at sea, like a big ship battle, boarding, fighting, etc.)

Then you have the captain of the boat Gang 1 is travelling with. He sails for a travelling company taking people from one dock to an island, and then further from that island to two different countries. But he takes his job very seriously. His motto is "I always get my passengers to their destination". He and his crew is kind of Gang 1, but also kind of another gang, Gang 7. Whatever, it is for you to decide.

Then you have the knight, who is wanted and has been through hell. He knows the destined one, and is kind of a failed mentor to him. He was supposed to guide him on his quest, but they were separated. Now he is coming back to help him. Despite being one man, we will refer to him as Gang 8.

Then you have the renowned, super-skilled bounty hunter, who is coming to retrieve the wanted Knight, or Gang 8. We will refer to him as Gang 9.

And finally, we have a powerful being who guards the mortal realm. There is a threat to the mortal realm, an invading God, which is why Gang 1 stole the sword to begin with. But the destined one within Gang 1 is merely a child, and the powerful being believes the sword is better in his hands, as he is a more capable fighter. We will refer to him as Gang 10.

And that's everyone. I am a big fan of Lock stock and two smoking barrels, and the way those kinds of narratives play out, when all the subplots, with all their unrelated characters, meet in a messy, complex confrontation. But I'm wondering, can this kind of stuff be too complex? Too complicated? Too disorienting?

Just so it is clear, all these characters have had sufficient time to have their stories told and their motives made clear.

It really depends on how you write it, how important all the components are, and if you can construct a consistent narrative journeying through the story.

Think back to all the big budget movies you've seen where there are giant armies and dozens of characters fighting on screen. The scenes are usually chaotic with lots of things happening at the same time, and in many cases it's just too hard to follow. But some of them work out well because they focus on specific narratives at a time, and use the rest of the battle as a backdrop. For example, in the battle of Helm's Deep, we spend a lot of time following the characters we know, witnessing things through their eyes, and it's okay if we don't see everything in the fight because we're focused on the parts that are important.

In written text, it can be a little more challenging because you can't show simultaneous action well, so there's a big risk that you end up with a muddled and confusing mess. But it's not impossible.

The Wheel of Time had an epic fate-of-the-world battle, "The Last Battle", where all the characters in the 14-book series got together in a last desperate struggle. In this fight, seventeen factions of light take on seven groups of shadow, and each force's story is told from the perspective of one or more characters associated with that group - the characters readers have followed along throughout the series. All the character stories and plot threads are given space for resolution, and the battle chapter clocks in at a massive 81,000 words, more than the entire first Harry Potter novel!

You don't have nearly so many individuals and probably won't need 273 pages for your battle, but some of the things that worked for Robert Jordan may work for your case.

It sounds like you have multiple point-of-view characters you've been building up through your story. Your battle is large enough, you can tell different parts of the battle through the lens of your major characters. Break it down into the individual narratives and you can relay it like a sequence of events taking place as part of the overall conflict. Similar to how you've broken it down in your question, you can start with a few groups and their skirmish, and then have the next group show up, and the next, and the next as things spiral into chaos.

But also take care to keep the narrative scope small enough so that it doesn't become overwhelming. If Gang 1 manages to escape from Gang 2 for a while, Gang 2 can temporarily drop out of the narrative while Gang 1 encounters another gang until it's time for Gang 2 to resurface again.

Just like in the movies, if you have too many characters on screen at the same time, then the individual actions of each get lost in the shuffle. If you can keep the focus on a few characters at any given time - say, a half-dozen or so - it'll be easier to follow along.

Let's take a look at the Battle of the Pelennor Fields in the Lord of the Rings:

First, we have the Rohirrim. Among them are Theoden, Éowyn, Éomer and Merry. Then we have Minas Tirith, with its various forces, and with Gandalf and Pippin as focal point characters. There's the events inside the city with Denethor, and there's Imrahil outside. In the middle of the fray, Aragorn arrives with Legolas and Gimli. And of course there's Mordor's army. So, similar to your example, multiple characters and multiple storylines converging on one battle.

What are we presented with? A confusing whirlwind, within which first one event than another is highlighted. We have no trouble following our multitude of main characters: each small scene is clear, and they are presented in sequence. But once we lose sight of a character, we do not know where within the tumult of battle he will reemerge. And the full account of the battle is explicitly not given:

for it was a great battle and the full count of it no tale has told.
_{J.R.R. Tolkien, Lord of the Rings Book V, chapter 6 - The Battle of the Pelennor Fields}

This is done deliberately. Tolkien took part in the Battle of the Somme, he knew that a battle is just too big, too confusing, you can't see all of it.

What does this example mean for your situation?

You have a lot going on. You want all of it to converge on one battle. But the fact is your "camera" can only focus on one mini-scene at a time. So you would need to break "what is happening" into small scenes you want to show, and show them in sequence. A lot can be happening off-screen while that one thing is going on on-screen.

If you try to show everything all at the same time, this will indeed be too confusing. A narrative is sequential by its nature.

But, you may well say, there is more than one thing happening all at the same time. True, but then you will need to figure out which one you show, and which one you only show the effects of.

You will also need to consider pacing: if the situation is supposed to be tense, you don't want everything to stall because you're trying to tell too many things at the same time. You want every small scene to contribute to a larger shape of things.

Figure out in what order things are happening, in what order you wish to present them (something might have happened, which your POV characters only find out later), how it all resolves itself. Then, write every small scene and let it play out: while this is the event you're highlighting, it is an island in the stormy sea, it is the one thing that's Happening. No distractions.

So, to sum up, you can have a lot of storylines converge into one massive event. This can be very cathartic when well-written. But making that situation well-written - that is a significant challenge. It would require considerable mental storyboarding.