Comment 1 for bug 1086763

Mundus strictly depends on gambas3 >= 3.3.0. The gambas2 packages are not needed at all. The gambas3 packages you are using are from version 3.1.1, which won't work. Besides being outdated because they are not maintained at all, they are wrongly packaged, but might work.

You have two options, you can either compile the newer gambas3 packages yourself (long and tedious process), or download the Mundus source archive and compile a gambas binary for your installed version.

For the later, download the source archive, extract, execute make, and then sudo make install (be sure to uninstall the Mundus .deb first)

I'm really sorry about this, but Gambas3 availability on Debian is scarce. We are in the process of creating a repository, but it takes a lot of time.