I just copied your script in to try it, and I had a few problems. The first one is with the box itself, it comes up with the multichoice and its a load of battle types (admitedly this is what I threw in there when I first made it, so it's my fault not yours) but is there a way to make this custom, or show the pokemon's names?
The next thing is that when I click on and recieve a pokemon, it says something like You received a ??????????! You still get given the pokemon, but that just seems a little odd.
Then it comes up with the Here's a pokedex + five pokeballs message twice, but doesn't gice you any pokeballs. Again this may be something I did wrong in the beginning script.
apart from this it works great, the pokemon that you are given is the one from the list that corresponds to the option picked (kinda) and you can only do it once. So those bits are fixed.