In a single instant, I basically experienced the loss of six games at once. I had transferred almost every Pokemon I owned from my Diamond to My Pokemon Ranch. This included almost literally every Pokemon from my Ruby, Sapphire, Emerald, Firered, Leafgreen, and Diamond. Fortunately, I kept the most important and powerful Pokemon that I use in-game, which averted me from losing my most coveted ones. But one day, lightning struck a tree across the road from my house. And what does that somehow do? It somehow destroyed the visual chip in my Wii. I could hear everything just fine, and could even hear my way through parts of a few games, but in the end, it was irreparable. So, I lost nearly all of those Pokemon since I had to get a new Wii. However, I still have some hope. The old Wii is still in my room as a memento. Perhaps someday I'll find somewhere that I can get it repaired, and then I'll finally be able to recover all of my old 'mons.
For the most part, the Pokemon were all just useless and I had only caught and evolved to complete the Pokedex. However, I did lose a few things that can never be replaced by myself: Ranger 1 Manaphy, and Ranger 2 Darkrai and Riolu. Still, I never used them, and only had them because of their value.