PokEdit is a legit site that can create flawless Pokemon, and I'm assuring that if I make a legit Thundurus, I can enter it in the US National Championship in Indianapolis. However, the site is always down, and I got the DNS Code right and everything. Whenever I access the GTS, my Thundurus never came. I checked the help page, and everything was perfectly fine. I have no clue what I could possibly be missing.
It might be that everyone is using it at the same time, causing too much workload for the site.
But it's probably just Sod's law.
And as trachy points out, it's against the rules to enter with such Pokemon.