MongoDB 3.6 introduces JSON Schema Validation, which extends Document Validation by enforcing schemas inside arrays and preventing unapproved attributes from being added. This feature allows for more powerful schema validation, including the ability to enforce business rules and prevent errors in data insertion. Additionally, MongoDB 3.6 introduces an expressive query syntax that enables developers to move business logic from the application layer to the database layer, simplifying their code base. The new features are designed to address data governance requirements while maintaining MongoDB's flexible schema architecture.