The equilibrium geometries and frequencies of endohedral complexes between H, He, Ne, Ar, Li, Li+, Be, Be+, Be2+, Na, Na+, Mg, Mg+, and Mg2+ and dodecahedrane (XΓ20H20) were computed at B3LYP/6-311+G(d,p). The majority have Ih minima; the exceptions, XΓ20H20 (X = Be, Be+, Be2+), have C5v symmetry with X localized against an inner cage face. Cage C-C bonds shorten slightly (<0.01 Å) and cage C-H bonds lengthen slightly (≤0.02 Å) in the series: M2+Γ20H20 → M+Γ20H20 → MΓ20H20 (M = Li, Na, Be, Mg). These subtle changes in dodecahedrane geometry are due to donation of electron density from the encapsulated metal atom into the C-C bonding and C-H antibonding endohedral complex HOMO, which has a structure closely resembling the LUMO (A1g) of dodecahedrane. The zero point-corrected inclusion energies of Li+Γ20H20 (Ih; -12.7 kcal/mol), Be+Γ20H20 (C5v; - 1.3 kcal/mol), Be2+Γ20H20 (C5v; -236.3 kcal/mol) and Mg2+Γ20H20 (Ih; -118.0 kcal/mol) are exothermic relative to their isolated components. However, all the endohedral dodecahedrane complexes are higher in energy than their corresponding exohedral isomers. Endohedral He and Li+ chemical shifts are 0.9 and 1.9 ppm, respectively. MΓ20H20 (M = Li, Na, Be, Mg) species possess lower first ionization potentials than the Cs atom (3.9 eV) and, therefore, are "superalkalis". Removal of dodecahedrane hydrogens can increase endohedral complex stability significantly. Thus, endohedral beryllium in the beryllocene complex, BeΓ20H10 (D5d) is 75.3 kcal/mol more stable than its isolated components, in contrast with BeΓ20H20 which is unstable by 127.7 kcal/mol. Dodecahedrane, HeΓ20H20 and Li+Γ20H20 B3LYP/6-31G(d) and B3LYP/6-311+G(d,p) absolute energies did not change significantly (<0.31 kcal/mol) when computed using either a pruned (75,302) or pruned (99,590) integration grid; with the addition of zero point energy the maximum deviation was less than 0.53 kcal/mol.