When comparing mruby vs GDScript, the Slant community recommends GDScript for most people. In the question“What are the best scripting languages for game development?” GDScript is ranked 10th while mruby is ranked 11th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Easy to embed in C or C++ programs.
Mruby is far more easy to embed in C or C++ programs than other scripting languages. No need to manage the stack, you just get the arguments back in your wrapper function and convert them from mruby to C with a single function call.
Pro Small
Pro A powerful, flexible OOP scripting language.
Mruby implements most of Ruby up to the 1.9 version. This means you get an extremely powerful scripting language with many features such as true OOP, lambdas and blocks, garbage collection, lexical scoping, mixins, built in arrays and hash maps, powerful string manipulation functions, ...
Pro Rather lightweight
Of all the Ruby implementations, mruby is the lightest and easiest to embed into your C or C++ game.
Pro Easy to learn
Pro Tiny runtime
Pro Similar to Python
Simple to learn and easy to read.
Cons
Con Smaller ecosystem than plain Ruby
Mruby is less popular than plain Ruby, and newer. It is less well documented.
Con Using the garbage collector needs some thought
The mruby garbage collector is more eager than that of Matz Ruby. It is sometimes neccesary to call mruby write barrier functions to protect allocated mruby memory from collection.
Con Godot only
GDScript is specifically designed for the scene tree design of Godot, therefore implementing it for different engines with varying architectures might be hard.