Download [Pokémon Stadium Editor here](http://www.mediafire.com/file/3c313pd2r1dhk06/stadium_editor.7z) (version 0.2). Windows only at the moment.
Source code: https://github.com/Guernouille/Stadium_Editor
Previous versions:
0.11: http://www.mediafire.com/download/0x92p1b27a98lbr/stadium_editor_011.7z
0.10: http://www.mediafire.com/download/vgr4mnuo94p9g4d/stadium_editor_010.7z

It's only compatible with USA .z64 ROM at the moment, other languages support will be added later on.
I'll clean source and make proper oop asap.

Randomizer, Type Chart edition, CPU Teams edition and Rentals edition, Base Stats and Learnsets are done. Scripts will be editable a bit later.

I'll write a proper description later!
For now, simply hover over the elements with a ¤ to have a quick description of what does what in the Randomizer.

A few screenshots:

Checking "Fixed PRNG" fixes the pseudo-random number generator, so you can share your randomization (might be useful for races). Copy/Paste the 6 PRNG Seeds to the other runners, click Fixed PRNG, then Randomize, and you're set.

Have fun !

Made a quick update tonight, adding Nickname edition and a better randomizer balance.
I also unchecked the "Gym Leaders Pokémon" by default, it wasn't supposed to be checked by default.
And a small display bug was fixed.

The download link in the first post has been updated. I'll write a quick tutorial someday, but by now if you have any questions, just ask them in this thread.

So happy to see you're still working on this. Adds so much replayability to the game.

I wish I knew how to make something like this myself, but I have no experience at all.
If i want to learn how to make an editor like this for Pokémon Stadium 2, where should I start?

My best advice would be to learn a programming language (like C++ or Python), and to learn MIPS if you need to disassemble parts of the game you want to edit (that is less important as CPU and Rentals Pokémon are already documented, but if you want to let the player edit scripts or other specific data you might need to do it).

Version 0.2 is out! You can download it here.
A lot of new features have been added with this version:

Randomizer

Pokémon data
• Base Stats, with min/max ranges for each Stat and Base Stat Total
• Types
• Learnsets, there are options to prevent ridiculous things such as Spore Electrode

Move data
• Base Powers, with min/max range (bar a few exceptions like Multi-Hits moves)
• Types (OHKOs will always have an immunity, provided you didn't randomize Types)
• Effects (Several parts of the AI check the moves IDs, so it may be a bit helpless sometimes)
• Accuracy and PPs are modified depending on the move data, with some randomness added to it
• Some moves won't be modified as they are hard-coded (such as Counter and Fixed damage moves
Automatic CRC fixing
• After modifying the Pokémon or the moves data, the CRC needs to be fixed) so that the game can start.
Fortunately, this randomizer does just that, so the game can be played on the fly on most modern emulators.
Project64, on the other hand, needs a little tweaking on your part after saving your modified ROM.
1) In Project64 folder, open the .rdb file in your Config folder with a text editor.
2) Find the entry for the unmodified Pokémon Stadium ROM you have
3) Copy-paste it at the end of the file
4) Replace the CRCs with the ones displayed on the randomizer after you saved
The entry for US Pokémon Stadium 1.0 (the only one supported at the moment) is this one:

Quote

[90F5D9B3-9D0EDCF0-C:45]
Good Name=Pokemon Stadium (U) (V1.0)
Internal Name=POKEMON STADIUM
Status=Compatible
Plugin Note=[video] (see GameFAQ)
Culling=1
Emulate Clear=1
Linking=Off

Miscellaneous
• Added a Progress Bar in prevision of the next version which will have a super secret feature :mrgreen:
• Coded the basis for other Laguages support
• Fixed a few bugs with the randomizer
• Fixed a few UI minor issues

CPU Teams
• You can rename the CPU Trainers
• The complete charset is implemented, you can use every character that is in Pokémon Stadium for your nicknames
• The tab order is in order Kappa

Battle Data
You can now edit:
• Pokémon Base Stats, Types
• Experience group, Base Experience, Catch Rate
• Moves Base Powers, Types, Accuracy, PPs
• Moves Effects
• High Critical Hit moves
• Critical Hit formulas
• Burn effect, Confusion and Paralysis odds
• Damage variance

Next update will include Pokémon Learnset edition, Damage Formula edition, and a secret playing mode Keepo

Wow ever since I found Stadium 2 rental offsets last year I had been asking everyone for someone to make an editor just like this! Funny thing was last night I finally gave up and manually edited all the moves. This is fantastic, are you still working on things?

Question is there a way to add different music into a rom like for the different battles that you do like for example instead of the mewtwo fight music you can have the glitchxcity remix of it playing in the background

I can't seem to find V1.0 anywhere. Would you happen to have a link to where I can find that specific version?