Very recently, a series of endohedral fullerenes Sc2O@C-2n (n = 35-47) were facilely produced. However, only two of them have been further characterized so far. Theoretically, we studied another discandium oxide endohedral fullerene without any characterizations, Sc2O@C-84, which is the second most-abundant species in terms of relative heights of all mass spectrum peaks. Two thermodynamically stable isomers with isolated pentagon rule-obeying cages were found, namely, Sc2O@C-2v(51575)-C-84 and Sc2O@C-1(51580)-C-84. This is the first case that an endohedral fullerene containing the C-2v(51575)-C-84 cage acts as the lowest-energy isomer, and it is the first report of a clusterfullerene containing the C-1(51580)-C-84 cage. The endohedral Sc2O cluster can keep its ideal structure after encapsulation, while both C-84 cages have deformed dramatically. Orbital analysis suggests that nudeophilic and oxidization reactions of both isomers should take place on the cage, while regioselectivity of Sc2O@C-2,(51575)-C-84 and Sc2O@ C1(51580)-C-84 is different due to their different characteristics of the highest occupied orbital distribution. Two-dimensional electron localization function and Laplacian of electron density maps unambiguously indicate strong electrostatic interactions exist between one scandium atom and the oxygen one. Meanwhile, overlaps of occupied metal atom orbitals and the cage ones along with Mayer bond order analysis identify that covalent interactions between a scandium atom and each C-84 cage cannot be neglected. At last, C-13 NMR, UV-vis-NIR, and IR spectra of both Sc2O@C-84 isomers were simulated theoretically. Because of their structural difference, all spectra between two isomers are significantly divergent. Consequently, these spectra are helpful to distinguish Sc2O@C-2v(51575)-C-84 and Sc2O@C-1(51580)-C-84 in further experimental characterizations.