Along with your answer, you can file what is called a counterclaim, which is essentially, a Statement of Claim filed by the defendant against the plaintiff. (See the information on Statement of Claim)
If your counterclaim exceeds the jurisdictional limits of the Magistrate Court, the case will be transferred to a court that has proper jurisdiction. Usually the entire case will be transferred. However, there may be some cases where the plaintiff's claim will remain in Magistrate Court and the defendant's counterclaim will be transferred separately.