I was mass releasing my pikachu's the other day when I accidentally released one that new fly, for a second I started to panic, but then my pikachu came back to me! I later found out that if a pokemon is the only one you have that knows a certain HM move you won't be able to release it. Ordinarily I would not be so foolhardy as this, but when I scanned through the pikachu's to get the special ones out I did it by level so anything 14 or 15 was saved. What I hadn't realized was that I had more than one level 15 pikachu because I left one in the pokewalker and it gained a level when I took it out, so I just put it in my pikawalker box to save it.....yeah, so that's the story about how I almost released my only pikachu that knows fly.