Mass. Gen. Laws ch. 244, § 8: Form of action; parties

Section 8. The entry may be made or the action brought by an assignee of the mortgagee. The action for possession may be brought, and shall be conducted as if brought by the original mortgagee. The mortgagor may be joined therein as a defendant irrespective of his estate in the land; but if he has no estate in the land and makes no defence to the action, he shall not be liable for costs.