What do you think of fics where someone has changed movesets of a Pokemon? (ex. Venonat used Hydro Pump; Starly used Bone Rush; Natu used Body Slam)
In my fic, I don't typically allow the pokemon to use things that they can't learn normally. However, I've only actually named one move, and that was Ember near the start. So it could technically be said that what my pokemon use aren't "moves" at all, but abilities that I find match their anatomy or whatever.
Sometimes I break the rules a little bit, though. For instance, there's a Houndoom in my fic, and at one point he uses Crunch, Fire Spin, and Faint Attack all at once. He lunges forward, bites down on a foe, wraps the both of them in fire, and then disappears with the enemy still in his jaws. He then reappears elsewhere with the enemy burned to a crunchy crisp. I don't really follow the "exchange of attacks" formula in the game, but it still sounds like something that would happen.
Now, if someone had a Venonat using Hydro Pump without an insanely good explanation (it's a Mew in disguise!), then I would be rather put off. If it completely defies logic, then it pretty much blemishes the fic rather badly.