Many transition metals have variable oxidation states. It is not limited to the first row.
They are flexible like that because the #(n-1)d# valence orbitals extend the number of available quantum states beyond those allowed by the #ns# valence orbital, and allow a wide range of states that can be stabilized by whatever is bonding to the metal, even when they don't use the #np# empty orbitals that much.
Having up to #10# quantum states available in a given set of #(n-1)d# valence orbitals, one can see oxidation states up to #+6# (such as #"Cr"#) and #+7# (such as #"Mn"#), with some few metals reaching #+8# (such as #"Os"#) or #+9# (such as #"Ir"#).
