How to set up CPU Routes in Battle Arenas#

Making battle arenas can be a ton of fun, what with making a closed battlefield to duke it out in one of the best battle modes in the series and all that. However, there is one thing that stops most people from making them, and the most important part: The CPU routes. Without working CPU routes (MEPO), the arena will not feel complete, and may malfunction. They are tricky to set up due to the fact they have to make rounds across the arena instead of just following a line. In this guide I’ll show you how to link up your CPU routes in your custom battle arenas. For this tutorial, I’ll use my arena, Moonview Plaza, as an example.

Before we start:

For battle arenas, we divide the routes in 2: The “main” routes and the “connection” routes. Main routes are parts where the CPU’s will go through, whilst the connection routes are the ones that link main routes to each other.
Blue: Main routes
Red: Connection routes

This guide assumes you are familiar with how setting up normal EPOIs works, so if you're not, I highly suggest checking this NKM tutorial! You will also need Mario Kart Toolbox for this guide.

Step 1: Setting up the main routes#

First, set up main routes on the areas you want CPUs to drive through. In here, I set a route going from one end of the center to the other. Go to MEPA and finish setting up the route.
Remember to also set the correct size of the routes so CPUs cover plenty of space.
Next, repeat this on all the individual parts where CPUs should go directly. Make a separate MEPA for each set of lines, don’t connect them all into one.
As you can see, I’ve left out all the spaces in routes where they should connect with each other.

Step 2: Setting up the connection routes#

These ones are even simpler, for now. Put a single MEPO point on all the areas where the main routes will link, and make a separate MEPA for each one, do not link them all together.
Your MEPA should look like this at the moment. Remember: The ones with one point of length are the ones that will link all routes together. With this out the way, let’s get to the tricky part: Linking everything together.

Step 3: Goes To/Next and Comes From/Previous on main routes#

First thing you’ll do is go to a main route, and look at the connecting routes that are near each end. In the picture, MEPO 1 of this main route has MEPO 16 near it. Similarly, MEPO 0 has MEPO 17 near it.
Go to the MEPA section, and look for the MEPA that connects the main route you selected, in my case being 0 and 1. On the right, look at the Comes From section, and type the route facing MEPO 0, which is MEPO 17, and in the Goes To section, type the route facing MEPO 1, which is MEPO 17. You should have something like this.
Do this for all the main routes that surround a connecting route, making sure the Comes From is a connecting point that is near the start of the main route, and the Goes To is a connecting point that is near the end of it. This is a time consuming process, so be careful when doing it, and have lots of patience. After that, everything should look nicely linked up; however, we are not done yet.

Step 3: Goes To/Next and Comes From/Previous on connecting routes#

Having linked up the main routes to the connecting ones, we are going to do the reverse. Look at a connecting point, and all the other points that surround it. In this case, MEPO 16 is the connecting point, surrounded by the following MEPO: 1, 3, 8 14.
Next, go to the MEPA of the connecting route, and on both the Comes From and Goes To sections, write all the points that surround it in any order.
Do this for each connecting MEPA. This is also time consuming and precise, so take your time and be careful. You’ll know if the routes are linking up well because the green lines get brighter.
After that, this is how it all should look:
With that, you have successfully set up the routes in your battle arena! Get in game and test them. Make sure that the CPUs take every direction possible. One thing to note is that at higher difficulties they’ll try and loop around areas that are close to the player, however this is not always the case. Stay in the game for a few minutes, in case they haven’t come across a faulty route early on.

If your track crashes, and warnings#

- If the game crashes in the middle of the battle, this means a set of routes has been linked incorrectly. It can be frustrating to know where exactly things went wrong, so verify all MEPAs carefully, and review the steps. You can also try monitoring the CPUs on the global map, and see where many of them are at once when the game crashes. That can give you a pointer to the route that’s not working.

- Always make sure to keep object 0069! This object controls several battle mode specific values and is needed for your track to work. Always keep it high above the CPU routes: If your routes are at Y=300, put them at about Y=500 or 700.

- The connecing MEPO/MEPA can only have a max of 4 connections, despite having 8 listed! Any further than this may cause issues.

And we’re done! From here on out, feel free to continue working on your arena as usual. This may all seem daunting at first, and it will depend on how complex your arena is, but as you do it more often you’ll get better at it. Good luck, and have fun!

Tutorial made by AltairYoshi on 5/10/20