Modding is only supported on the Linux and Windows versions. Thank you.

Creating a mod should be possible on Linux, but is a bit difficult... so I reccommend using Windows and will be outlining Windows usage with Visual Studio here.

To get started, you'll need:

• .NET Core 
• Visual Studio
• UnityEngine.dll and MinoEngine.dll (I recommend you look at the source code for MinoEngine, here.)
  • UnityEngine.dll can be found in your Unity install directory, under Editor/Data/Managed.
  • MinoEngine.dll can be found in the game files (Data folder) under the Managed directory.

Steps:

• Create a new C# Class Library 
• Add a reference to UnityEngine.dll and MinoEngine.dll (In Visual Studio, Project>References>Right-click>Add Reference>Browse)
• Name your class, making sure to add using UnityEngine and using MinoEngine at the top.
• Make your class implement IRuleset/IMode/IRandomizer (depending on what you want to make)
• Implement all class members how you'd like!

An example (Default SRS) can be found here.