Vanilla - no mods. This includes 1.23, 1.24, 1.21 etc. Games are not separated by their version since they do not change the speedrunning experience. You should update to 1.23 if you have versions 1.20 to 1.22 though (also necessary for installing plus). It's provided in the resources tab.

Plus 3.0 - an old version of plus that retains all of the old physics quirks and bugs, but fixes longstanding bugs like Lori unable to grab copters and potentially crashing on cycle after grabbing a shield. You can download it over at the resources tab.

Plus 4.0 + - While most physics are the same, many speedrunning bugs and physics quirks are removed, such as; Hyperboosting, Spamming Spazkick at the bosses, Devan phase skip, the robot boss freeze glitch. However, it's known to be more stable with Wine.

It also has some weird bugs/physics quirks, like getting stuck inside walls with crates, and Spazzes kick getting a little burst of speed after kicking enemies/bosses with flying properties.

How to install plus 3.0 If you already have plus installed, replacing plus.dll will do. Be sure to keep a backup of the other in case you want to switch back. If you don't: Copy and paste all the contents to the corresponding Jazz2 folder. I recommend ctrl + a to select all. Then, use plusifier.exe. This will create a plus version of your game - Jazz2+.exe. Note that this will break the autosplitter, so I recommend renaming it and the vanilla version to something like Jazz2NoPlus.exe. Newer versions The installer will do the work for you, just select the directory lol.

Where to download: Put get.jj2.plus into the address bar - it'll appear in your downloads rather than take you to a new page.

DISCLAIMER: **Plus does NOT work with the LK Avalon version of JJ2. This is the default version GOG provides and found on many pirate sites. ** You can tell by the intro splash screen and Polish language support provided by default. To install plus via GOG, check out this handy guide: https://gog.jj2.plus/