TenForward: Where Every Vulcan Knows Your Name

@treczoks@lemmy.world @toynbee@piefed.social Found it! But it wasn't Mark Twain, it seems to have been the artist Waldo Peirce!

https://en.wikipedia.org/wiki/Practical_joke#Famous_examples

One practical joke, recalled as his favorite by the playwright Charles MacArthur, involved American painter and bohemian character Waldo Peirce. While living in Paris in the 1920s, Peirce "made a gift of a large turtle to the woman who was the concierge of his building". The woman doted on the turtle and lavished care on it. A few days later Peirce substituted a larger turtle for the original one. This continued for some time, with the surreptitious substitution of bigger turtles into the woman's apartment. The concierge, beside herself with happiness, displayed her miraculous turtle to the entire neighborhood. Peirce then replaced the turtle with smaller and smaller ones, to her bewildered distress.[23] This became the storyline of the 1990 Roald Dahl children's book Esio Trot.

He seems to have been quite the joker:

In 1910, Peirce enjoyed a bit of local notoriety when his prank on friend John Reed, the American communist who is buried in the Kremlin walls, became known and circulated. The duo had booked passage on a cattle freighter from Boston to England, but as the ship was leaving Boston Harbor, Peirce apparently decided that the accommodations were not to his taste. [citation needed] Without a word to anyone, he jumped off the back of the ship and swam several miles back to shore. Reed was then arrested by the ship's captain for his alleged involvement in the disappearance of his traveling companion and thrown into the brig. When the freighter eventually arrived in England, Peirce was at the dock waiting to greet his friend Reed. After his swim back to shore, or, by another account, being picked up by a lobster boat, he had then taken a faster ship to England. In later accounts, Peirce's John Reed story seemed to evolve and shift, to the extent its veracity may never be truly known. One further embellishment to the story is that Peirce had swum in a multi-mile swimming contest at Harvard a few days prior.[4]

https://en.wikipedia.org/wiki/Waldo_Peirce#John_Reed_prank

Sounds a lot like Roald Dahls story Esio Trot. Protagonist makes downstairs neighbors tortoise "grow" with a magical spell (tortoise backwards, replacing it with other tortoise) to win her heart. In the end, tortoise is too big so he "shrinks" it again so it'll fit back into her house.