Nothing except for understand idiots going saying Cresselia is uber.
Everything is easy to understand, as long as the IV/EV part is out of the way, the rest just came to me:
- Every Pokemon has a number between 0-31 in all stats, if it picks 0, it sucks, and if it picks 31, it's good.
- In other words, Pokemon has to born good, or born suck.
- Retards like a Modest Rhyhorn should not exist and be shot in sight.
- Some exceptions can be accepted like if a Machamp has 4 in SA.
- Predictions are important, but don't overpredict.
- Use all your pieces effectively, remember your opponent's pieces.
- Deoxys-S and Skymin are uber.
That's all you need to know about Pokemon D/P, it's a insultingly simple concept, but punishingly difficult to pass the luck and planning.