The cards -- usually indicating Matt was "having a good time" -- were postmarked from New York, Florida, Mexico, Hawaii and Paris.
Mrs. Walton initially thought she was receiving the postcards by mistake. But after reading a few of them carefully, she decided they must be linked to her missing inflatable bat.
Some postcards promised Matt would return in time for Halloween.
Sunday night it happened, with Matt returning as mysteriously as he disappeared. He was delivered at 11:30 p.m. by a neighbor claiming three people she met on the street asked her to deliver the package.
The Waltons are still puzzling over that. But a dozen photos in the package with Matt left no doubt the intrepid bat had been seeing the world.
The snapshots show Matt relaxing on a sandy beach, snorkeling in the ocean, cooling off in a Virgin Islands hotel swimming pool and hanging out in front of a Honolulu police station.
Though various pepole appear in the photos with Matt, there is no one the Waltons recognize. "We're baffled," Mrs. Walton said.