Others having a similar issue had either a corrupt download of the jar containing file, or at least missing subfolders of that downloaded file (like the libs folder).
Try to validate it's the full file and you have extracted all properly.
I come across another post and forgot to insert it here, but it is saying I need the jJavaFX installed. Well I am extremely new to Linux so I have the zip file of the javafx, but I'm three sheets to the wind on installing it correctly. Ive tried extracting it to my usr/local directory, fired up netbeans but its not registering any JavaFX file.
I did run the other option of installing through lutris but it is next to impossible to read and last time I attempted to run it, (which was months ago) minion would simply crash.
I like the instructions from Dolby, but it sounds like I need to install the JavaFX for it to properly install. the .jar
UPDATE: I'm just using the Lutris install instructions to run Minion. I am not going to worry about JvaFX right now, don't need to.