How do I install mods for the freeware version?

I beat Hell and the Wind Fortress, and I`m looking for something new, but I have no idea how to make mods work in Cave Story. I don`t see a "mods" folder, but I have a "data" folder generated by the mod I downloaded and a "profile.dat" that I can`t open.

 

Mods are self-contained, all you need to do is open Doukutsu.exe (or whatever it'll be called) from the mod you downloaded

 

I`m not sure what that means, though. Do I need to put Doukutsu.exe in a different folder, or do something with the data file? I`ve tried just launching the game, but it just plays normally, and the mod says to "overwrite the files in my copy of Cave Story with the versions in the newly created data folder".

 

I`ve tried just launching the game, but it just plays normally, and the mod says to "overwrite the files in my copy of Cave Story with the versions in the newly created data folder".

This isn't the conventional mod then, usually a mod just comes as is and there's nothing that need to be 'installed' or placed elsewhere.
You're better off asking what you have to do at the thread of this mod.

 

BTW if the mod is "Cave Story Randomizer v0.8a:
Just extract "Cave Story" and "Randomizer" to your desktop.
Then open up "Randomizer" and start "Cave Story Randomizer [Open Mode] v0.8A.exe"

Now drag "Cave Story" into the program window as it asks.
Now in the "Randomizer" folder, it should have created a "Data" folder.
Copy that into your "Cave Story" folder.
That's all. Now you can play the randomized game by opening "Cave Story" and launching "Doukutsu.exe"

You can tell if it's working if the title screen says Cave Story Randomizer.

Spoiler: general mod info

Most mods will have the entire game, so you just unzip it and play it.
But, in the case that the mod does not contain the game... generally you need an unmodded copy of the original free version, and then put the mod into the unmodded copy where it should overwrite files.

Basically the game folders are setup like:
INSERT_GAME_NAME_HERE -> Data
Data -> Stage; Npc;

(Profile.dat btw is the game's standard save file, it belongs in the INSERT_GAME_NAME_HERE/Cave Story folder, or whatever it is called.)

If a mod is looking for a "mods" folder:
That belongs in INSERT_GAME_NAME_HERE or Cave Story folder, or whatever it is named. Try that. If that doesn't work...

You'll probably need to download the dll mod loader first. Then overwrite "mods"...
https://www.cavestory.org/forums/threads/dll-mod-loader-alternate-music-mod.13879/
But this is only required if the mod somehow requires the dll mod loader and is not including all the "mods" files...

Just in case: Wind Fortress does not exist in the free version btw. That would be Cave Story+. Most mods are meant for Cave Story.

 

Yes, mods aren't anything applied to the game itself; the way you download it is just an edited version of CS in full, so you don't patch it to anything like how you would a SMW romhack, for example. If the "data" folder and "profile.dat" are all you have, you might want to replace the data folder and profile.dat (or just put it in the folder if you've never saved on that CS folder) and use the Doukutsu.exe and DoConfig.exe, config.dat, and window.rect (the Manual files and OrgView are unnecessary and can be deleted) already in the folder.
Hope this helps.