R2Modman can be installed here, [thunderstore.io] but if that link doesn't work, you can find it on GitHub at h t t p s : / / g i t h u b . c o m / e b k r / r2modmanplus. Remove the spaces to access in your web browser.

This is the main mod manager we're going to use for Cult of The Lamb, and it has tons of support with other games. It's good with everything, and will have everything you need (besides Nexus support but we'll get there).

Looking up Cult of the Lamb mods can give you Thunderstore, which will also direct you to downloading r2modman.

Download the COTL API there, since that is a library and dependency which most mods use. Also download BepinEx, and if you want you can download its configuration manager.

BepInEx is here, [thunderstore.io] or you can look for it yourself if the link doesn't work. It should be one of the first mods on Thunderstore, actually -- so it's very easy to find if you go to the last page and scroll down.

Setting up r2modman and installing your mods is pretty simple, so I won't be talking about that here. When you go to Thunderstore after setting up r2modman, there will be a shiny new "Install with Mod Manager" button. Now you can install mods without having to do it manually.

When you go into Cult Of The Lamb with mods enabled, you'll probably notice that Achievements are disabled.

How do we stop this? It's quite simple. Just go to your settings, and then go to your Mods section.
Then, turn "Don't Save Achievement" off. This setting disables all achievements. If you have it disabled, you're good.

That's about all you have to do. Now you can install mods and play the game with achievements as much as you want.

Time to start installing from the Nexus, which isn't as simple as Thunderstore.

(side note: I'm not much of a support guy. I'm still relatively new to modding myself, so I can't give the best advice - but I'll say what I'd do to try and fix these issues.)

PROBLEM: My game automatically starts when I try using Thunderstore/r2modman, and I can't install any mods.
SOLUTION: Back up your game files (Steam should do that for you,) and attempt to reinstall your game. Also try using Thunderstore's manual reset button (please back up your saves, I'm not responsible for any missing data.) and uninstalling + reinstalling that too. It's like the age-old saying of "Have you tried turning it off and on again?"
R2ModMan has a built-in mod installer that comes from Thunderstore.

PROBLEM: Mods don't work on my game/mods aren't functioning properly.
SOLUTION: Attempt to uninstall/reinstall the mods. Your settings might not save, but r2modman has a built-in config backup creator (I'm pretty sure it does, at least. If it doesn't, try to take screenshots of your settings for the mod you're fixing.)

Usually Nexus doesn't have support for r2modman as a downloader (unlike MO2,) so the best thing to do is just manually installing the mods.

To do this, follow the mod's install instructions. Profiles for r2modman can be found by going to:

Settings -> Browse profile folder

It's just that simple. Now, drag and drop your unzipped mod into where-ever it needs to be - there you go, you've installed a mod for COTL from the Nexus!

If you wanna do ReShade stuff, here's what to do:

1: Download reshade at https://reshade.me/ .
2: Click Cult of the Lamb's exe file.
3: When prompted with the graphics it uses, select DirectX 10/11/12.
4: Check what plugins you want and select them.

You now have ReShade set up for Cult of the Lamb in just a few minutes! Now you can tweak the game to make it look how you want.
This includes tons of video effects to make the game uniquely your own with a bunch of other stuff. It's awesome, check it out!

This guide is made to be followed easily and also for those who've never installed mods for this game before.

I plan on making a ReShade tutorial in the future! That will be linked here when the time comes.