In Hacked Pokemon Tower Defense, you can gain more money, gain way more EXP, and Pokemon are catchable in one hit! (Boss Pokemon are still not catchable) The front page also says 'Hacked Version" in red. Pokemon trained, used or caught in the Hacked Version bares a distinct "Hacked Tag" and widely reduces the value in the trading communty.
Mystery gifts: To get access to a mystery gift on hacked pokemon tower defense you have to:
Click get mystery gift which then brings you to a new tab, the place is called play tower defense- games.com
After that, you log in with your info, then this time you will be able to validate your code. But that is only if they are still valid.