We assume meta-programming is less used in embedded environments.
We have moved following methods:

 * Kernel module
   global_variables, local_variables, singleton_class,
   instance_variables, instance_variables_defined?, instance_variable_get,
   instance_variable_set, methods, private_methods, public_methods,
   protected_methods, singleton_methods, define_singleton_methods

 * Module class
   class_variables, class_variables_defined?, class_variable_get,
   class_variable_set, remove_class_variable, included_modules,
   instance_methods, remove_method, method_removed, constants

 * Module class methods
   constants, nesting

Note:
Following meta-programming methods are kept in the core:

 * Module class
   alias_method, undef_method, ancestors, const_defined?, const_get,
   const_set, remove_const, method_defined?, define_method

 * Toplevel object
   define_method

`mruby-metaprog` gem is linked by default (specified in default.gembox).
When it is removed, it will save 40KB (stripped:8KB) on x86-64
environment last time I measured.