At first I wanted to start Compiz WM from the CLI with something like "startx", but failing to figure that out I went to using lightdm. I followed the instructions for making the .desktop files and all that stuff on the Ubuntu Help Wiki for CompizStandalone and managed to get compiz to show up in lightdm, but I get an error when trying to log into compiz WM:

: unable to launch "/usr/local/bin/compiz-session" X session ---
"/usr/local/bin/compiz-session" not found; falling back to default session.

then when I click okay it loads the cinnamon desktop (I normally use MATE+Compiz). I've triple checked all the paths are all correct. I've been alternating between trying this on my Mint computers and an Ubuntu mini install on a spare HD, same exact issues on both.

My main goal here is getting the Compiz WM standalone to load on an Ubuntu based machine.

PS. I'm using Mint 19 and Ubuntu 18.04 LTS if that's important.

Are these the instructions that you're following?: https://help.ubuntu.com/community/CompizStandalone

If so, they include the creation of /usr/local/bin/compiz-session, but your error message says that it is not found. Does it exist, and did you make it executable?

Yep, I forgot I had to make it executable. Everything works now.

Nice one. Enjoy!