Challenges in unstructured mesh generation for practical and efficient computational fluid dynamics simulations. An efficient and robust unstructured mesh generator, the Mixed-Element Grid Generator in 3 Dimensions (MEGG3D), has been developed to create good-quality meshes quickly and easily. MEGG3D has several key components for computational fluid dynamics (CFD) simulations, such as: (1) file compression with open-source data-compression utilities for faster file transfer; (2) three automatic local remeshing methods to modify existing hybrid volume meshes for additional components; (3) an easy-to-use hybrid surface mesh generation method to represent high-curvature surfaces with high-aspect-ratio quadrilaterals; and (4) multiple and suppressed marching direction methods to improve the quality of semi-structured elements in convex and concave corners, respectively. In this paper, those key components are introduced with practical examples.