It worked. Wow! I thought my mono runtime was broken!
Awesome, thanks! It did give me two errors when I ran it, even though the editor opened. Here's the whole output, just in case:
INFO: Using configfile: /home/USERNAME/.config/supertux-editor/settings.xml
Error: Couldn't load configfile: Could not find a part of the path "/home/USERNAME/.config/supertux-editor/settings.xml".
ERROR: Couldn't load configfile: Could not find a part of the path "/home/USERNAME/.config/supertux-editor/settings.xml".
INFO: Creating new config from scratch
INFO: Supertux is run as: supertux2
[INFO] /build/buildd/supertux-0.3.4/src/supertux/main.cpp:223 [/home/USERNAME/.supertux2] is in the search path
[INFO] /build/buildd/supertux-0.3.4/src/supertux/main.cpp:223 [/usr//share/games/supertux2] is in the search path
INFO: Data files are in: /usr//share/games/supertux2
I think I recognize this error, but it's been so long since I've used the editor that I can't remember. Thank you very very much for helping. I really appreciate it.