Danius88

You can either directly edit the save file in the RAM (though I don't know where the slates are stored, you would have to research it), or you can use some AR codes to beat the last temple more easily. I used this codes:
- Battle Codes: 1 Loop Capture
- Battle Codes: Attack Never Hits Line
- Temple Codes: Activate Dual/Quad Switches Alone
- Temple Codes: Quest Time Never Decrease
- Movement Speed Multiplier v2: Movement Speed x4

You can find these codes in DeadSkullzJr's NDS(i) Cheat Databases. Keep in mind that the temple codes only work for the US version, but the save files are compatible between versions. It will take a lot of runs, but with these codes it will be way easier!

16 minutes ago, Paco said:

Thank You! I'm trying to do it, yet the Hex Editor can't find 0x1EB4C maybe am I searching wrong? Which Hex editor you recomend for such task?

Thanks again for your help!

Use HxD and press Ctrl + G and you will find it. 0x1EB4C is a location of the file, not an actual value.

I would like to share some documentation I made last year regarding editing some obscure features of the Gen 5 games and I was able to succesfully edit the Unity Tower floors, the Geonet locations and all the results from the passerbies and surveys.
I made a somewhat messy in-depth Excel file explaining everything I was able to find, but I will explain it briefly here.

The Unity Tower Block (Block 29 in both BW and B2W2) stores data of the Unity Tower floors you have unlocked, the recent players's NPC you have encountered and all the Geonet locations you can view in the globe from any Pokémon Center. Your own country and subregion data is stored in the main trainer block. The most interesting thing about this is that there are 102 unreleased countries/sovereign states to choose in the Geonet that were unavailable, but works the same as the regular countries! These locations were previously documented by @suloku in his BW Tool program, in which you can edit the country location of the NPCs from the Join Avenue. They were unnoticed despite some of them being hilarious, like Vatican City or North Korea.

The Passerby and Survey Block (Block 63 in BW and 61 in B2W2) saves the results of all the passerby answers and surveys. They can be edited to eassily achieve S+ Rank in the Passerby Anaylytics HQ from Castelia City.

I will also submit my own edited blocks that everyone can import to their save files using the mentioned BW Tool. I hope the excel file is understandable enough, feel free to ask me if anyone has any doubt! This was the first time I tried to document something, so I apologice in advance if something is slightly wrong.

B2W2 Documentation.xlsx B2W2 Block 61 (Passerby and Survey).bin BW Block 63 (Passerby and Survey).bin BW-B2W2 Block 29 (Unity Tower and Geonet).bin

12 hours ago, Paco said:

I have no idea how to change that. Can you help me? I just need to change 1 value at the encounter with Aura/May at the volcano.

Open your save file in a Hex Editor and go to 0x1EB4C. You will see there the Pokédex number of the Pokémon you have in the volcano scene.
For example, Metagross's number is 376 in decimal = 178 in hexadecimal using any hex calculator. If I wanted to write Metagross, I would overrwite the next 2 bytes with "78 01". 

I'm not sure what are the next 2 bytes (0x1EB4E-1EB4F), I think they are the gender/shiny form. If you want it to be shiny, you can write "03 00" there.

Edit: Remember to open and save the save file in Pkhex to fix the checksums.

The Pokémon's data shown in the credits are stored at 0x1EAF0. The game saves your EC and the Pokémon IDs for each event.

 You can also make them shiny/mega/alternate forms tweaking the ID.

Without using any kind of external devices, the only way to re-activate the events is by doing glitches. Keep in mind the Pokémon won't be legitimate because you are not getting them in the intended way, but they will be legal, except if you catch Mew in a non-Japanese game.

Here's a tutorial of how to unlock Deoxys and Mew events on a Spanish Emerald game, there's probably more guides on how to do it on other languages.

I couldn't find any way to re-create a custom Battle Institute test, but I was able to edit a DLC test record! In B2W2, the Battle Institute records are stored in the block 0x23700 - 0x237A7.