The unique properties of diamond make it an appropriate material for various cutting-edge scientific and industrial applications. The progress in the development of new diamond based technologies is inseparably linked to research and development into the synthesis and growth of this material. For instance, developing new routes for the fabrication of diamond containing defects with specific optical, electronic and magnetic properties is crucially important for the emerging quantum technologies. Recently it has been found that diamond synthesis under high-pressure, high-temperature conditions using catalysts based on magnesium demonstrates a number of intriguing characteristics such as an extremely high growth rate, unusual micro- and macro-morphology of crystals, and effective doping of diamond with Si and Ge impurities. In this highlight, we will describe the major features of the growth, morphology, internal structure, and defect-related spectroscopic characteristics of diamonds crystallized using Mg-based catalysts under high-pressure, high-temperature conditions.