Various fixes and such.
There's a fancy wad called REKBONUS by brightentayle that is autoloaded when dropped in the REKKR Sunken Land folder, you can find it discussed here: https://www.doomworld.com/forum/topic/90862-rekkr-v116/?page=24
Short of it is: Adds the bonus ep from the original mod release as an episode 5. Needs to be named "REKBONUS.wad" or it won't work.
10/18/2021
Source: Steam Community (opens in a new tab)