Since we're allowing this, I'm going to get it out of the way quickly.
Here is species flavour text for all games up to Sw/Sh. BD/SP missing doesn't matter because the entries are the same as D/P, and PL:A missing doesn't matter because the flavour text in that game is invariably long.
I used find and replace in Notepad++ to remove \n and \r from the document. I also dealt with some encoding problems; Excel, for some reason, doesn't read in UTF-8 by default so I manually converted the garbled characters, such as é, ', :, ♂/♀ and –. I also removed all languages other than English.
The answer turned out to be fairly simple. The shortest Pokedex entry is Kyurem in White, with 49 characters: "It can produce ultracold air. Its body is frozen." The next shortest is Shellos, which has an entry with 56 characters that is repeated in a few games.
