The development of multifunction nanoparticles proved their worth in the field of the discovery of drug/gene delivery, nanotheranostics (in-vivo imaging, coinciding diagnostics), in external healing intercessions, designing a nano-bio interface, and to do desired alterations in nanotherapeutic. Every so often, the cellular uptake of multifunctional unlike cobalt [Co, CoO, Co2(CO)8 and Co3O4] nanoparticles (UCoNPs) influenced cellular mechanics and initiated numerous repercussions (oxidative stress, tempted DNA damages, cyto-genotoxicity, and chromosomal damages), in pathways, routes and generate dysregulating factors in the biochemical transformations exceedingly. Unlike dimensions of UCoNPs-cell interfaces, their physical features (size, shape, shell structure, and surface chemistry), possessions on cell proliferation and differentiation are the vital whys and wherefores, which are hereby, specifically identified as the key causes responsible for nanotoxicity. In this review, the UCoNPs intricacies (cyto-genotoxicity, clastogenicity, and immunomodulatory), nanotoxicity, and associated repercussions have been highlighted and discussed. The interpretation of quantitative structure-activity relationships, chemical transformations, biological, and toxicological analysis are discussed. The concerns and influences of multifunctional UCoNPs on different cell mechanisms (mitochondria impermeability, hydrolysis of ATP, the concentration of Ca2+, impaired calcium clearance, defective autophagy, apoptosis, and necrosis), and interlinked properties (adhesion, motility, and internalisation dynamics, role in toxicity, surface hydrophilic and hydrophobicity, biokinetics and biomimetic behaviors of biochemical reactions) have been summarised. Various applications i.e. bio-imaging, cell labelling, gene delivery, enhanced chemical stability, and increased bio-compatibility are highlighted concerning apoptosis, necrosis, and nanobio-interfaces with suitable examples.