I tried dual-booting Manjaro from my Ubuntu install, since VMs were slow on my machine at the time and I wanted to give Manjaro a try.
Manjaro wouldn’t boot (X11 sessions crashes on boot), and then when I returned to Ubuntu, I got dropped straight to the GRUB rescue shell because I had shrunk the partition from the Manjaro installer, and it had fucked up the Ubuntu install :/ so instead of two OSes I had none