Mutant Core is the base bundle of emoji in the Mutant Standard.
It is the Unicode Standard, with various modifications and omissions.
Mutant is a small project, so not all emoji can be explicitly accounted for as the Unicode Standard updates every year. Instead, Mutant Core consists of a series of symbols that are added, changed or excluded versus Unicode Standard.
Mutant Core can also be added to via communication extension bundles - Mutant Spectrum and Mutant Form.
Additions in Mutant Core versus Unicode Standard are designed to be backward compatible with Unicode Standard, with additions only being non-RGI emoji. PUA encodings and non-standard ZWJs are only used in the communication extension bundles.