The Secret of NIMH 3

The Secret of NIMH 3 was a planned third film, Originally, Timmy to the Rescue was to be the second installment of a Secret of NIMH trilogy. The third film would have taken elements from the third book R-T, Margaret, and the Rats of NIMH.

Plot
Would have taken elements from the third book R-T, Margaret, and the Rats of NIMH in which Timmy and friends help two human children named Margaret and Artie.

Why It Was Cancelled

 * 1) The plans for the third film were canceled due to Timmy to the Rescue's negative reception.
 * 2) MGM Animation closing their studio when its founders Paul Sabella and Jonathan Dern left to make SD Entertainment.

Result

 * The sequel was permanently cancelled.
 * In 2015, MGM had re-acquired the rights to produce a new film based on the original novel Mrs. Frisby and the Rats of NIMH, and is planned as a CGI/live-action hybrid to the novel, The film will be produced by the team of Daniel Bobker and Ehren Kruger, with screenplay by Ice Age series writer Michael Berg. It will be James Madigan's directorial debut.