Rule of Criminal Procedure 4

A. Issuance.

 * 1) If one or more affidavits filed with the complaint establish probable cause to believe that an offense has been committed and that the defendant committed it, a magistrate or constable (hereinafter "issuer") must issue an arrest warrant to an officer authorized to execute it. An issuer may issue more than one warrant on the same complaint.
 * 2) Exception for fine-only offenses.  In the case of a complaint filed regarding a fine-only offense, the defendant shall receive a summons from the officer issuing the citation to make his or her initial appearance before the court.

B. Form.
A warrant must:
 * 1) contain the defendant’s name or, if it is unknown, a name or description by which the defendant can be identified with reasonable certainty;
 * 2) describe the offense charged in the complaint;
 * 3) command that the defendant be arrested and brought without unnecessary delay before a magistrate; and
 * 4) be signed by an issuer.

C. Execution and Return.

 * 1) By Whom. Only an authorized officer--a member of a guard organization, military personnel, or deputy--may execute a warrant.
 * 2) Location. A warrant may be executed within the jurisdiction of the Kingdom of Stormwind or anywhere else the Laws of Stormwind authorize an arrest.
 * 3) Manner.  A warrant is executed by arresting the defendant. Upon arrest, an officer possessing the original or a duplicate original warrant must show it to the defendant.
 * 4) Return.
 * a. After executing a warrant, the officer must return it to the magistrate before whom the defendant is brought in accordance with Rule 4. At the request of an attorney for the Crown, an unexecuted warrant must be brought back to and canceled by a magistrate.
 * b. At the request of the Crown Prosecutor's office, a magistrate may issue a copy of an unexecuted warrant to the authorized officer for execution or service.

D. Review of the Warrant.
In any case where a warrant was issued by a constable, the defendant may request, during his initial appearance, that the magistrate holding the hearing review the warrant for defects. Upon such a request, the magistrate must schedule a pretrial hearing for this review. If the warrant is found to be materially defective, all evidence acquired through the warrant is inadmissible at trial. If the warrant is found to be without material defect, the defendant will not be permitted to raise further objections to it.

Commentary
This rule only applies when the cart has arrived before the horse and a complaint is filed before the defendant is arrested. It's perfectly fine to do so, as long as the defendant's player has consented in advance (which usually happens during a previously agreed plot).

Getting a warrant thrown out, or any sort of defect in the arrest process, does not invalidate the entire case, however. You need a better argument than the Scooby-Doo Defense.