In Bava Metzia 21b, there is a mnemonic given which I find quite odd - פמג"ש ממקגט"י ככסע"ז . See http://www.sefaria.org/Bava_Metzia.21b.18?lang=he&layout=block&sidebarLang=all
The way I see it, the point in mnemonics is to help people remember things. eg. Detzach Adash Beachav helps remember the names of the plagues. In this case, the mnemonic seems particularly difficult to pronounce, let alone remember, so it doesn't seem to be doing a very good job. Not only that, but what is the particular importance of remembering these cases? The Gemarah doesn't make such widespread use of mnemonics all of the place as far as I am aware so why here?