1. Syntax and Composition: Groovy is a full-fledged programming language that allows for complex logic and operations, including loops, conditionals, and functions, while Mustache is a logic-less templating language primarily used for rendering HTML. Groovy provides more flexibility and functionality in terms of programming capabilities, allowing for a wider range of operations within templates.
2. Variables and Scope: Groovy allows the declaration and manipulation of variables with varying scopes, including local, global, and class-level variables. Mustache, on the other hand, does not support variable declaration or modification within the template itself, relying solely on the passed context during rendering. This limitation in Mustache simplifies the logic within templates but restricts the manipulation of data.
3. Template Inheritance: Groovy supports template inheritance and hierarchy, allowing for the creation of reusable components and layouts through includes and extends. Mustache does not have built-in support for template inheritance, making it less suitable for complex layouts that require modular structures and components. Groovy enables a more modular and organized approach to template design.
4. Conditional Statements: Groovy includes conditional statements such as if-else and switch-case which allow for dynamic content rendering based on specific conditions. In contrast, Mustache does not support conditional statements directly in the templates, requiring the logic to be handled outside the template before passing the data for rendering. Groovy provides more control and flexibility in determining the output based on dynamic conditions.
5. Extensibility and Customization: Groovy allows for the creation of custom functions and methods within templates, enabling greater extensibility and flexibility in handling specific use cases and functionalities. Mustache lacks the ability to define custom functions or methods within templates, limiting customization options to the available built-in features. Groovy offers more opportunities for customization and enhancement of template functionalities.

In Summary, Groovy provides a more robust and flexible programming environment within templates compared to Mustache, offering advanced features such as custom functions, conditional statements, and template inheritance.