People who have never seen it probably don't believe that Abbott and Costello Meet Frankenstein is a good movie. By a happy coincidence, Universal had Abbott and Costello under contract and all those Universal horror characters needing a new outlet. So you take the two comedians, toss in Dracula, the Wolf Man, and Frankenstein's monster, toss in Lenore Aubert as a femme fatale, and voila! They had the original Wolf Man, Lon Chaney, Jr., reprising his classic role. And most notably, Bela Lugosi made only his second (and last) appearance as Dracula. There were some classic A&C skits, and the scares were actually real. And Abbott and Costello were still in the prime as one of the most popular comedic duos around.
This set off a series of "Abbott and Costello Meet" movies. There was Meet the Killer, Boris Karloff, and Meet the Invisible Man, and Meet Captain Kidd, and Meet Dr. Jekyll and Mr. Hyde, and Meet the Keystone Cops.
Which takes us to Abbott and Costello Meet the Mummy. It was the last picture they made with Universal, and their next-to-last movie, period ... Lou Costello died in 1959.
It wasn't very good. The Mummy was played by stuntman Eddie Parker, and he wasn't scary. The other stars were people like Michael Ansara and future Mel Cooley Richard Deacon (he wasn't scary, either). Marie Windsor livened things up a bit, and the last fifteen minutes or so are fun in a frantic way. But Bud and Lou look tired. In the credits, their characters are listed as Pete Patterson and Freddie Franklin, but during the film, they just call each other by their actual names, as if it didn't really matter (it didn't). The whole thing plays like a Crosby-Hope-Lamour Road movie, only a weak one. Peggy King popped in for a song, and in an incongruous moment, there's a giant lizard of some sort (it wasn't scary, and the special effects weren't special).
So it's easy: if you have a hankering for something like this, Abbott and Costello Meet Frankenstein is out there. Don't bother with The Mummy.