To perform the Fishing Sprite Glitch in Harvest Moon DS, all you have to do is hire the fishing sprites in Winter to fish at the Beach. There is a chance that you will end up with billions of G in-game, when you get paid.
This has been patched in Harvest Moon DS: Cute.
Corrupt save files
On rare occasions, saving while the fishing sprites were active would result in your save file becoming corrupt and unplayable.