  This is a companion paper of arXiv:1909.11492 and arXiv:1912.01930. We prove
an equivalence relating representations of a degenerate orthosymplectic
supergroup with the category of twisted $Sp(2n,{\mathbb
C}[\![t]\!])$-equivariant $D$-modules on the so called mirabolic affine
Grassmannian of $Sp(2n)$. We also discuss (conjectural) extension of this
equivalence to the case of quantum supergroups and to some exceptional
supergroups.
