Diamond is a unique mineral widely used in diverse fields due to its remarkable properties. The development of synthesis technology made it possible to create diamond-based semiconductor devices. In addition, doped diamond can be used as single photon emitters in various luminescence applications. Different properties are the result of the presence of impurities or intrinsic defects in diamond. Thus, the investigation of the defect formation process is of particular interest. Although hydrogen, nitrogen, and boron have been known to form different point defects, the possibility for large impurity atoms to incorporate into the diamond crystal structure has been questioned for a long time. In the current paper, the paramagnetic nickel split-vacancy defect in diamond is described, and the further investigation of nickel-, cobalt-, titanium-, phosphorus-, silicon-, and germanium-related defects is discussed.